If every time someone treated us badly, abandoned us or any other act that hurt us, we started being bad, I honestly don't know where humanity would be, and unfortunately it's at a very bad level. You decide what you think is best for your life, do you want to have multiple partners? Go ahead. But there's nothing better than being a good person, both for yourself and for others, if someone has managed to destabilize you from this level that you want to go down to a low level that is using people (which it is) then you have to work much harder on yourself, forget about others, you are you and you only control what you do and think, you don't control how they will react towards you or what they think. I don't know what happened to you to come to this conclusion, but I'm sorry for your pain. But there's another thing, it's impossible to live and never get hurt or disappointed, life is like that, it has its ups and downs, you'll end up hurting and disappointing people too. Don't be another idiot, be yourself, that GOOD person! Leave when you realize you don't fit in. In the end, even if it takes a while, you'll be recognized and guess who will recognize that? Other good people who are worth being around. Everything passes in life and that's great.
Stay safe !