Why do some men lie and cheat when they're in a very happy relationship?

My friend is dating a guy who is head over the heals in love with her. But what I noticed is he’d be avoidant, or if he is confronted with something he’s guilty of he’d just avoid it and say things like “I love you baby <3” or rather than actually solving it. I also dated a guy like this and he’d consistently seek other women when he is in a different area in town or at a party even though he really was crazy about me. And when I’d catch him and ask him why he did it or ask him for honesty (because he’d avoid it) he’d give me one liners or get defensive or just laugh and say he loves me. I met men like this before and honestly have no idea whats wrong with them. It seems like the key issue here is that they see women as more of objects rather than human beings they can connect with. My friend who is dating that guy and I both had panic attacks when we caught them in action and then having to confront them reasonably and calmly gave us avoidant, mocking, accusatory or manipulative answers and nothing more. It was very frustrating I ended up crying thinking how can someone be so irritating, disrespectful and avoidant when the person they like is hurting and wanting to communicate.

Its a very touchy issue for me but all I’m asking is why do some men do this and behave like this when they really care about a woman who shows them affection too? It just makes no sense to me other than like i said, their twisted vision of humans and women.