Most Helpful Guy
Don't get back together with him first of all, once the trust is broken you can only try to find someone new. It might be hard to accept but the truth simply is that it will always be in the back of your heads if you bet back together.
If you know you can't stay faithful you can only go for non-serious relationship. But if that's not what you want, I would say that you need to learn to stand up for yourself, say no to people more often. If you easily break under preassure you clearly need to work on that for the sake of future relationships.