We don't always have to give them their marching orders. Whatever you've been through and whatever people say, you never know what's going to happen and you have to do what's right for you.
If a guy has cheated and broken you heart, yes he's a rat, but that doesn't mean the rest of the males on the planet are the same. Besides, you must know at least one girl who has cheated - it doesn't mean all women cheat, right?!
Give others a chance and don't label all men as cheats: learn to trust another. It takes time and effort, but you'll get there.