When we first meet Dante, he's in a relationship with Kippy, Dolores's roommate. They're relationship is getting the long distance treatment since college began, and before long, Kippy moves on, without telling Dante. He keeps mailing her letters, though, and Dolores intercepts them. Reading these letters, she falls in love with the boy who calls himself in his yearbook: "Saint Dante" and lists his pastimes as "Milk and Cookies, praying for sinners" (13.56). Granted, we're suckers for milk and cookies, too.
Dolores loves him because he's unlike any man she knows. His father cheated on his mother, and he promises Kippy that he "would never be a WOMANIZER like him" (13.97) (famous last words, let's say). He's sweet and sensitive, a.k.a. a man she can dominate, not the other way around. Even when he sends Kippy nude photos, Dolores sees them as an offer, not as a demand. Dante feels safe to her.
Years later, Dolores finds Dante's address and moves in across the hall from him. Totally normal, right? As an adult, he's a high school English teacher. Dolores doesn't tell that she knows him or that she's seen him naked—she doesn't really tell him anything—and they enter into a relationship. Eventually it turns out he loves sleeping with his students and correcting other people's grammar. So not teacher of the year material.
Dante's a complicated character, because he is nice to Dolores a lot of the time. He's understanding with her foot phobia (Jack touched her feet a lot before raping her), he's romantic and passionate, and he's good in the sack. But being nicer than all the other losers in her life isn't enough to make him husband material.
He doesn't want kids, mostly because he's still a big kid himself, so when Dolores gets pregnant (after lying to him about being on birth control), he convinces her to get an abortion. He offers to go with her to the clinic (the nice-guy part of him coming out again), but she hates him because the abortion is his idea, so she tells him to leave. Even though she'll never forgive him for this—ever (she even names the baby before the operation)—she agrees to marry him afterward.
It's all downhill from there (shocking, we know). He gets fired from his job for molesting a student, which he keeps from Dolores for a while, then he takes Dolores's savings and buys a van. He also turns abusive. He's mean to their only friends, Paula and Boomer, because they're successful in ways that he's not, like buying a house, even if it is a trailer, which Dante calls a "glorified Big Mac container" (23.24). Such. A. Hater.
He's a vegetarian and poet, the pretentious kind that makes you hate both vegetarians and poets and every piece of poetry ever written. He takes out his frustration with himself—over legit things like getting fired and being a terrible writer (he writes a poem about masturbating at Dolores's grandma's funeral)—on Dolores. And much as Dolores is a pill, she definitely doesn't deserve this since these things have literally nothing to do with her.
Dante really looks down on our main girl. He's pretentious, calling her "unfettered" (25.86) and saying that he appreciates her "simplicity" (25.89) because he's oh-so complicated. He's about as complicated as ninth-grade algebra: It seems difficult when you first get there, but once you know the right formula, it's a snap to unravel all the problems.
Dolores eventually catches him with Sheila, the student he gets fired over, and leaves him. But when Dolores's grandma dies, he drives to her to help take care of her. Maybe he hates loneliness just as much as she does—or maybe he's just an opportunist, wanting a place to stay in rent-free.
Eventually she gets fed up with him. The masturbatory funeral poem pushes her over that edge, and she tells him off at Burger King and they get a divorce. Guess she finally does get to have it her way. Good riddance.