While one might be forgiven for thinking that her problem with him is that he has a problem with understanding that she's a person in her own right with friends, family, likes and dislikes instead of a collection of body parts whose sole existence is oriented around servicing a goober, what really drove a wedge between them is his tendency to not notice that it matters that he checks out other girls and it matters more that she's taking a distant second to cars. This means that she finds someone who does a better job of faking that he gives a shit about her as a person and Mike runs away from her screaming because she hurt him and destroyed him publicly by seizing something no woman should have because that leads to him doing his own damned housework, the lily: the initiative.
We see this pattern repeat itself when he doesn't understand that it might bother Rhetta that he can rant for months on end about dating a girl from out of town and moving on from beyond the confines of home and so on and so forth while she's expected to remain pining away for him like a fantasy projection instead of a person. This leads to
- her finding better options than a boorish child-man and
- him wailing about false hearts who say cruel worlds like "I'm a person too and I have needs."
Since he's always going to be the dismal little sooky-baby howling that his MOMMA doesn't LOVE him because she doesn't see the need to hover over him non-stop, his only option has to be someone who'd do just that and excuse every last knavish act of his to piss her mother off.