Banned for an awesome theme, and an awesome game 
banned for thinking you can take into consideration more than what is present.
Nothing which has yet to occur can be taken into full account. Sure, he can say 'I want to wait for someone I think is much more serious' and he can do that. I don't care. But to wait with the uncertainty that anyone else will come along leaves him just floating. If he's interested in the boob girl (keep on mind that qualifier), he can ask her if there's anything serious between them. No one is obligated to be in their given relationship, just obligated to be honest about it. If she likes him more, she should see if he's interested and, if so, dump the other guy. The other guy won't mind in the long run because he'll know she wasn't that into him.
If it turns out he wouldn't mind hooking up with his old flame, then flame on. What he does is totally up to him. I wouldn't say shit if he didn't want to start a conversation because he never takes any of my advice anyway. I'm just making conversation with a little humor thrown in here and there. I don't expect anything to come of what I say.
The cool thing is that he could talk to boob girl and she could leave her boyfriend to be with him and they could have a long lasting relationship which leads to them joking with their grown grandkids about how she use to flirt with him like that. Or they could hook up and have a relationship that takes them just beyond graduation, where they decide to elope and spend six months of their lives learning to hate one another and ultimately divorcing with the consolation that they never had kids to make things more complicated. Or she could accidentally slip out of her bra, land a full on boob over his forehead and he leave discharge in his pants.
First of all, the "boob girl", like you call her, is named Hannah.
Secondly, I think Mishayla (his crush), also has big boobs. Same goes for Liz, although I am not so sure about that.
3rd, I reeeeeaally dont think that Xer07 is that much of a "physical" kind of guy. He doesnt care so much about sex, and I really admire him for that.
Moreover, Xer07 is always deeply in love with Mishayla. That said, I wouldnt expect anything less than him staying faithful to her, even though they never were nothing more than friends.
Also, you have to keep up with Xer07's stories in the Chatroom, because obviously you've missed out a lot.
LOL @ the slipping out of her bra thing
A really good one 
Aaaaanyway, I dont want to talk any more in Xer07's behalf, so I am just gonna shut up, let him do it for himself.
Oh and, you are Banned for making a big post without offering any real advice, good sir 
That would be all.