Why aren't guys stable?

I used to see this guy and finally let him go because he wasn't appreciating me. I gave him many chances and he eventually would go back to him ways and I was over it. Since then, he has kept coming back to me and just won't give up. I kept telling him no until you change or not for a really long time cause maybe we need space to grow up especially him. So he would stop then just hit me up again. Eventually I hung out with him because I did miss him company. But for me it was only as friends. He had told me was seeing someone else and she had left too. He did exactly what he was dong with; he kept going back to her. I'm like why can you just be stable with one girl and at one time? Do you have to chase her away? This goes for other guys too. I heard my childhood friend was trying to get in contact with his ex gf who he cheated on various of times (how do I know? cause it was with me) but of course she would say no. Why do guys have to cheat???? Why can guys ever have enough??? This other dude looked super obsessed with my friend. He would do anything for her. To everyones eyes, it looked like he was all for her. Then we saw screenshots of him asking this girl (the friend of the guy I was seeing) for bjs after he would come home from my friend's house in the morning. I was honestly devastated. I lost so much hope for guys from then on. It really shows how much guys can be scumbags. You never know what guys are up to. And yes yes it goes for SOME girls but come on the majority of cheaters/liars are guys. Whyyyyy. It's sad and mind-f*cking how guys are desperate little creatures deep inside when they act all confident and innocent. Sometimes I feel like yes the guy (in general) is a good guy and really loves his girl but naturally, he needs more and needs some enforcement to prevent him from doing anything. Thats one of the reasons I believe girls can be over-protective abd look "crazy" to guys because we want to show them we cannot be fooled and will always be on our toes. At the end of the day, I wish I could still be with that guy I was seeing especially how he keeps contacting me and not in an obsessive way but it looks like he cares now. But it's so hard to trust guys.