What to do???

So I’m married it’s not a happy marriage. Hasn’t been for some time now. Well, last year I was just done and slept with a friend of ours. We told my husband it happened and that I wasn’t happy in our marriage. My husband said we could come back from this but at the same time, he was seeing someone else. I and this friend have since hooked up three more times. The friend told my husband that he didn’t like me or see me like that yet had continued to sleep with me or other things. I just don’t get it. After we sleep together he goes mia until the next time we are around each other. Well, this last time we slept together was in my fertile window. And now I’m just thinking of everything that could go wrong. Do I let this guy in on what’s going on or do I just wait until I know if I’m pregnant or not? Also, why do you think he goes mia after doing things??