Help me understand why when a man who want to treat you like you're supposed to be some girls go for the opposite

I knew a girl who had a baby when she was like 15 the father still wants to be with her but she wants to sleep around.

then another girls situation is a great guy she said she was in love with they already live together so he wants to do the right thing because he really Ioves her so he asked her to marry him she kicked him out now how backwards is that

My question is everyone says they want a man who will treat them right won't cheat on them just someone who adores them, then when they get it they cheat on them,or say they are boring. But you know they are the only one who really care about you and will treat you right , then when you meet someone else whose a complete a**hole you complain then

WHAT DO YOU WANT I MEAN REALLY