CONCOURSE — A Bronx man texting his boss to let him know he'd be late for work was stabbed to death by his jealous girlfriend — who thought he was texting another woman, police and family members said.

Norberto Cruz-Valentin, 21, was repeatedly stabbed in the torso in the midst of a fight with his girlfriend Kristal Delvalle, 23, inside their shared apartment at 1064 Carroll Pl. on Monday afternoon around 3 p.m., according to police.

The fight began after Cruz-Valentin texted his manager at the Equinox Fitness in Midtown Manhattan on Monday morning to tell him he would be late. Delvalle became enraged because she thought he was texting another woman, according to Gary Collins, Cruz-Valentin’s stepfather.

Cruz-Valentin was pronounced dead at Lincoln Medical Center, police said.

Delvalle, who has no prior arrests, was arrested at the scene and is expected to be arraigned on charges of manslaughter and criminal possession of a weapon, police said.

Relatives said the relationship between Cruz-Valentin and Delvalle was extremely tumultuous.

Cruz-Valentin was arrested last March and charged with aggravated harassment and assault, according to the NYPD. His family did not dispute claims that the two would fight and hit each other, but added that Cruz-Valentin was not the sole instigator of these confrontations.

“They were just both hotheaded, and she gave as good as she got,” Collins said, adding that Cruz-Valentin was a loving, kindhearted man in an extremely volatile relationship that they hoped to get him out of.

“He was a hard worker,” Collins said. “Everybody that knew him said he’s a hard worker and a nice kid.”

Cruz-Valentin would often show up with injuries, according to Israel Oliveras, his manager worked as a maintenance man at the Equinox Fitness on 50th Street and Broadway.

“He always came into work with ... bruises and physical cuts, things like that,” he said.

Oliveras still praised Cruz-Valentin's work ethic, calling him one of the best employees he had who was punctual and well liked by gym members and coworkers.

“Knowing right now that I’m going to walk into my locker room, and he’s not going to be there, it's pretty hard,” he said.

"He was a good kid," Oliveras said. "All he wanted to do was work, and he actually loved that girl."

Llanel Soto, Cruz-Valentin’s grandmother, described him as a sweetheart with a phenomenal amount of patience.

“You could say anything to him and he never was disrespectful,” Soto said through tears.

His mother Janet Cruz said her son was a very happy person but that she did not get to be with him that often while he was dating Delvalle.

“I only used to see him in the job,” she said. “She didn’t want him to be around me.”