Sure, you can be worried all you want. This days it's almost natural to be. The thing is, is that no matter what you do or how much you worry if he is going to cheat on you, he's going to cheat on you. You might be able to postpone it sometimes, but eventually he'll find a way. I know it is hard, but you will be miserable living a life with someone that you can't trust. If you trust him then don't worry about it, but Yes, inviting yourself wouldn't hurt either.