I would of thought that u shouldn't have to have a talk about being faithful pretty much I thought that it was expected unless both said that they wanted an open relationship or if it wasn't serious. That doesn't seem to be the case; this is about him hitting on her sister's sister-inlaw. jr1017, I would just tell him that a relationship is based on trust, communication,love,and also forgiving one another or trying to. Now the trust has faded the only thing u can base it on is communication. I'll just call her ur sister-inlaw for short -k- anyway she told u that he said this was something he thought of for a long time right? so even if he can't remember what happened he knows what he was thinking before that night. Tell him that you need to hear his side. We all one time or another wonder what it would be like to be w/ someone else in an innocent way or not so innocent it's human to wonder but we know acting on it is a big difference. Tell him if you are going to find a way to get over it, it is time he steps up finds his courage and tell u the truth because u know what he said to her. This will hurt u both more u then him, because he won't want to pay the price but ur trust is already ruined and how can u fix it if u know he was thinking of her and won't step up and admitt the truth. This is the worst and biggest test of ur love for him to try to forgive him and u are giving him a chance to fess up. The truth will set u free (well kinda) I told my husband that the damages were done and now all I was left with knowing her side. I was very calm on the outside. I told him how can I trust you now if u won't tell me the truth. I was left  knowing that it really did happened and still he denied it. I didn't want to hear what I feared but  I had to and there is no avoiding that. Tell him it won't make it worse even though it might but if u want to know the truth I guess u gotta trick him a lil. You deserve to know he should give u that much to tell u. Your test is to see if you can forgive, his test is will he be man enough and say the truth or keep on being a liar killing ur trust even more and not try to repair the damages he had done. I hope it will work. I know your pain and i really feel for you. Do you want to stay w/ him or have you already split up ? Also has he ever cheated on you before ? Talk to u later. stay strong and just keep breathing even though it is hard to when your heart is broken.