I know plenty of people with divorced parents who took the whole thing easy and were not emotionally crippled by it.
Hell, there's those of us (raises hand) that would have had a far better life had their parents got divorced instead of staying together in a loveless (at times violent) marriage out of some sense of (1) not letting the other one "win" (2) "You don't get divorced, that's not proper".
My parents finally separated during my senior year in High School. It never got violent, but the non-stop arguing was awful. Of course by the time they did separate, I had school, sports, a job, car, girlfriend so I was hardly home anyway, but when I was home, it was quiet.
That's fine, but it has nothing to do with making a lifelong committment to another person. Of course there are very mature 22 year olds. There are a hell of a lot more immature 22 year olds. I dont have the numbers, but I;m sure they would show a correlation between age and length of marriage. In today's world, I wouldn't even think of marriage until I was 30, at least.
Guys who are into anal are into causing pain, if she's up for it, fine. If not, that's her call. As for the "getting on top" thing, well that should be up for negotiation. But guys who stray are looking for something that they're not getting at home and if he's out putting it in strange places, he's going to bring home something besides flowers, if you catch my drift. Having said that, however, there's not much you can do other trhan make it clear that you're there to be supportive if and when she decides to leave the guy.