Baby mamas

I don't understand some Men and women seriously...my friend she's obsessed with a guy that cheats on her has a baby from him..and his forever bad mouthing her to his friends and cheating on her..and yet she goes and falls pregnant AGAIN!! Seriously why do men/women do things like this??are women really desperate thinking let me try and catch him with the second baby and still doesn't work out..and guys oh wat the hell I will always be having side chicks