seddm answered:

Star never loved Tom, she kept being with him because… their relationship worked. After Lake House Fever and after Curse of the Blood Moon there were no major issues in their relationship anymore, but there was nothing particularly deep or important either. Star and Tom never shared a moment of emotional intimacy and growth together, their relationship has always been extremely shallows and surface level: to Star, initially a bandaid for the Marco shaped hole in her heart which then became a “constant” in her chaotic life, “Tom is my boyfriend”, it was easy and believing that helped her not think about other stuff. To Tom, Star was initially THE source of external validation and then, when he started improving around the end of S3, she still remained a huge source of his self identity, because as shown by Junkin’ Janna and as said in A Boy and His DC-700XE, he doesn’t really have anything else going on in his life beside “being Star’s boyfriend”. And that’s clearly not a good thing.

Now that the part of Star’s life that began in S3 ended, the "honeymoon” began to break down: she has been forced to take a long hard look at her life and she’s not that sure this is what she wants anymore, she’s scared but also excited about finding out what she wants from life. And now Tom is going on a solo trip, while Star is going to stay far from Tom for some time, and this is most likely going to help her former realize that he can be happier and feel way more fulfilled when he’s not relating all his self identity to being Star’s boyfriend,

and Star is going to realize that she doesn’t really miss Tom, that a huge part of their relationship was based on habit and circumstances, and not on GENUINE desire, on what she REALLY wants, which is absolutely in contrast with the theme of the season.

It’s true, Star and Marco might not actively have romantic feelings for each other right now but that’s just because this show is compartmentalized to a fault, ROMANCE and EMOTIONAL INTIMACY are completely separated until they aren’t anymore. It’s like Curse of the Blood Moon: dancing for one minute without distractions, lost in each other, brought Star and Marco from “we have feelings but we hate them and we want to get rid of them” to “I like this and I deeply regret entering the Severing Stone because I realize now that I really care about these feelings”. So they need just a small spark, a push that face them with no possibility of escaping with the question “what do you feel for each other?” once they’re both single, and they’ll inevitably have to admit and embrace the truth, that they’d do ANYTHING to be together and they care about each other more than anything else and that they deeply love each other.

So there’s no “deserve”, there’s only “badly matched relationships”, as Jackie said in Britta’s Tacos.

There’s no “suddenly conflicted”, it’s just that for the first time in months Star had enough time to question the things she has going on in her life, instead of embracing them as they come because too busy with Eclipsa and Mewni.

And there’s no Curse of the Blood Moon confirming that the curse caused those feelings, because it’s clear that they slowly developed over the months in a natural way, and from a more meta level Star left us with the most leading question in the whole show, one that can only have “It wasn’t.” as an answer.