I can't do a reading without hearing the person's voice, but my heart is telling me that you need to take some time to yourself and establish who you are. I know you really love him, but you need to love yourself first, and decide how much you are willing to compromise yourself just to be able to say you are with someone. While you may not trust her (and I don't blame you) the question is, why is he going to the friend's house without you? And why is he going if he knows she will be there? And again, if he knows she'll be there, why not take you with him or avoid the place?
He needs to grow up if he 'has a problem where he doesn't think about what he's doing at the time". I believe you deserve better.