This is sort of par for the course when you consider that for the first month, he wouldn't act on his impulse to talk to her because he was too stupid and gutless to ask "Who is this older boy to you?" and assumed that Rhetta's big brother was her boyfriend. Assuming things sort of bookended their relationship in a way that would have heaped shame on him were he capable of it.
This is because of why she went from the one and only to being a windshield he'd splatted on: she acted on his vague threat to play the field when he was away and simper that the girl he was with meant nothing to him so should mean nothing to her by suggesting that they go on break in order to avoid any sort of complications. She might have talked to him and his parents but what she never did and still doesn't understand is that Mike expects to be betrayed and humiliated going into a relationship. Hell, he even thought Deanna was going to cheat on him to make him feel like a fool. We'll see why when Lynn has Gordon explain what love is.