I need advice!

Me and my husband was separated for about 6 months and we saw different people.....but now we are back together and thing are rough I can't get the other girl he was seeing off my mind I don't know why I feel like she got things from him that I never got and I feel bad for thinking this! I wanna move on with him and be happy but it is like every where I turn it reminds me of them.....how do u move past some thing like this? How do I stop thinking about them be together?