BOSTON -- Imagine dedicating your life to a single objective for 10 years. You sweat for it and you suffer for it and you bleed for it. Then you walk away from it, taking care to set up your successors to continue that pursuit, because you consider that responsibility as part of your legacy. Finally, the conditions are right for them to achieve that dream ... and it turns out you're now the one trying to prevent its realization.

This is the scenario that David Backes, current Boston Bruins forward and former captain of their Stanley Cup Final opponents, the St. Louis Blues, has been wrestling with for the past week. The hero has played long enough to become the villain, in the eyes of his former team.

"The part of me that's regretful is that we didn't get to a Final or win a Cup in my time that I was there. That's a huge regret," Backes told ESPN on the eve of Game 1 in Boston. "They're the opponent now. I have to think of them as such. But I had about six days to wrap my head around that and to say that, 'It's us or them.' And that's really helped me."

It can't be overemphasized how much bringing the Stanley Cup to St. Louis for the first time in the franchise's history -- or, failing that, at least making the Final for the first time since 1970 -- meant to David Backes for most of his adult life. He bled blue: Drafted by St. Louis 62nd overall in 2003. Debuted with the Blues in 2006. Earned the team captaincy in 2011. Helped it grow from a basement dweller back to a perennial playoff contender.

The closest he came to achieving the dream was in his final season before signing with Boston as a free agent in 2016. The Blues won seven-game series in their first two rounds, then lost in six games to the San Jose Sharks in the Western Conference final.

"The buzz in town was extraordinary. If we had made that next step, I don't know what would have happened. We would have blown the roof off the arena," recalled Backes, 35.

Instead, it ended with him weeping in the St. Louis dressing room. It wasn't so much the loss as it was an anecdote he shared at the time about Steve Ott, who is now an assistant coach with the Blues.

"He'll kill me for telling you this story, but in Game 5 [against San Jose], I'm not feeling well. And Steve Ott brings me something to make me feel better, knowing that he's the guy coming out of the lineup if I can play," he said after Game 6 in 2016, his voice quivering. "That's the kind of guys we have in here. Just stories like that. Guys blocking shots. Sacrificing their bodies. The heart's in there. The ability's in there. It's just that we came up short."

There are 11 players from that 2016 conference finalist on this edition of the Blues. They didn't come up short this time, beating the Sharks in six games to advance to the Final.

The only thing standing in their way now are the Boston Bruins -- and David Backes.

"I remember the feelings I had. It was a little bit of sadness, a little bit of regret, because I thought that was a group that could have won a Cup," Backes said on Sunday. "I wish it was alternating years, so I could cheer for the Blues one year and they could win a Cup, and we could have our opportunity and they could cheer me on, and we could all have one to our names. But it's come to this: Them or us."

Among "them" is one of Backes' best friends and his protégé on the Blues, Alex Pietrangelo. Which has made this all the more awkward, for both of them.

David Backes (42) forged a bond with Alex Pietrangelo (27), the man who would replace him as Blues captain. Darcy Finley/NHLI via Getty Images

"Oh, here we go," Pietrangelo said with a sarcastic eye roll.

About three questions into his scrum at Stanley Cup Final media day, someone brought up David Backes to the man who replaced him as captain. Pietrangelo had been answering some variation of this question -- about personal feelings being put aside, about the surreal nature of having to go through Backes to win the Stanley Cup -- since the end of Game 6 against San Jose. His answer hasn't wavered.

"We both have a job to do. And we both have the same goal at the end. We're going to go out there and do what we have to do," Pietrangelo said.

2019 Stanley Cup playoffs Miss a game from the 2019 Stanley Cup playoffs? Want to experience a game again? Every playoff matchup is available for replay on ESPN+. Watch now »

Backes was a few years into his career when Pietrangelo, 29, arrived as a full-time player in 2010. The two became fast friends, to the point that Backes was in Pietrangelo's wedding party in 2016. It was that weekend when Backes told Pietrangelo that he was leaving for Boston, and it felt as though one chapter of his life was beginning as another was ending.

Some weeks later, Pietrangelo discovered a note from Backes that he had tucked into the sunshade of Pietrangelo's car. It was a letter about being a captain, about being a Blue, about being an adult. They laughed about how long it look Pietrangelo to discover what Backes assumed would be a letter he would read that weekend. But Pietrangelo eventually found it, and he read it, and it meant everything.

"When I got there, we were dead last in the league with the first overall pick, not doing too well. In the last five years of my time there, we were potential Stanley Cup finalists each of the years. We ran into hot Chicago teams or L.A. teams that were winning Cups on a regular basis and didn't allow us to reach that goal," Backes said. "So, any advice I could give to him that would be able to continue that work that I believe I had some fingerprints on, I wanted [Pietrangelo] to continue that, no question."

Blue general manager Doug Armstrong believes this friendship benefited Pietrangelo as a captain.

"Oh, I would say that they have a great friendship. They're both great men off the ice, great family men; they shared a lot of the same values away from the rink. I think that as David came in, we made him captain when we got there, he grew into it. Thrusting Alex into it too was a team in transition," Armstrong said. "I thought Alex -- every day he's becoming more comfortable and better at what he's going through. Going through what he went through this year, having -- for the people that don't know, he had triplets in the summer and then got off to a bad start, there was a lot on his plate. But he was able to put it all in its proper perspective and lead us at the most important time of the year."

Evelyn, Oliver and Theodore were born to Pietrangelo and his wife, Jayne Cox, on July 21, 2018.

"I think everyone that's a parent will say it's the best thing that's ever happened. That's the case for me. I guess you gotta grow up pretty quick when you have kids, right?" Pietrangelo said.

For Backes and his wife, Kelly, it was a joyous moment too, having seen what their friends had experienced in trying to start a family, which Pietrangelo chronicled in an emotional essay for The Players' Tribune.

In The Crease Postgame analysis and highlight show airing each night throughout the season from Barry Melrose and Linda Cohn. Watch on ESPN+

"That's another part of this game. The wives grow friendships. When they had some issues with pregnancies before [the triplets], my wife was supporting Jayne in different ways. Now, they've got three kids at once," Backes said. "The issues they had getting pregnant, staying pregnant, it's a big blessing all at once. Three amazing kids, and a great mom and dad to raise them."

As their husbands draw their battle lines in the Stanley Cup Final, the wives have remained in contact.

"They've exchanged texts seeing what's going on with each team and how things are being run. Outside of that, I don't want to know about it. They can make however many wagers or friendly bets they want to make," Backes said.

But when it comes to texts between the Blues and Backes, it's radio silence.

"Friends on the St. Louis Blues are now cut off, officially. If they text me, it's going to fall on deaf ears," Backes said. "If they get a text back, it might be from my daughter and it will be very incoherent."

Backes began his NHL career with the Blues back in 2006-07. Mark Buckner/NHLI via Getty Images

Backes said he and Kelly "grew up" in St. Louis. They had their first daughters there. They started their Athletes For Animals foundation there and were a visible part of the community. Backes said that, like so many other former Blues players, he could see his family settling there after his playing days are over.

His emotional ties to the Blues and St. Louis remain intense, but not nearly as much as when he initially left as a free agent.

"I'm very fortunate that this didn't happen my first year out of there. I'm not going to lie: My first time back in St. Louis, I think I was numb from the emotions. Going around, seeing security guards I haven't seen all year or people in town. Man, I thought this is a place that really touched me in my life," Backes recalled.

"From age 22 to 32, there's a lot of growth as a person. I feel like I made a little impression on the city. But the city made a huge impression on us. Thankfully, it's not that first season back there. You kind of get those warm and fuzzy feelings out of your system. Not that they're gone, but they're just not experienced like the first time."

Pietrangelo agrees that enough time has passed so that this is all slightly less surreal.

"If you had asked me that before he signed his contract, maybe. But it's been a few years now. We've played a lot against each other in the last couple of years. We've both gotten our heads in a different spot," Pietrangelo said.

At the end of this series, Pietrangelo and Backes will shake hands. One of them will skate off to the dressing room for the last time this season. The other will remain on the ice to hoist the Stanley Cup for the first time in his career.

Win or lose, there will always be the lingering bit of regret for David Backes that he couldn't help the Blues achieve that dream when he was there.

"But the truth is that there's been 52 years of groups of guys that probably have that same regret," Backes said of St. Louis.

"It would have been a great city to win a Cup in. That said, I don't know if there's a bad city to win a Cup in."