I need help!!!!

Okay so I told my husband how I’ve been feeling and having urges to sleep with a girl... I e neve done it or anything like that... well someone had mentioned trying a threesome and when brought to his attention at first he was like no I don’t like that idea which is fine because I didn’t know how I felt about it... recently he started talking about doing one... well he mentioned trying to ask my sister and I was against it from the beginning.. he had my phone one day and messaged her on my phone asking her how she felt about it. She agreed.. okay so backstory like 2 months before we got married we went on a family vacation with all 3 of my sisters and my parents and some family friends... we got home and everything was fine we got married and then a few months later it was brought to my attention ruin that a rumor had been going around work that while on this family vacation he had asked my sisters for a threesome while I was sleeping... we talked about it and after trying to cut him with a knife and going ape shit I decided to tell myself it was a rumor and that’s all... okay Fast forward to now... he messaged her off my phone to ask if she would join us and to me if felt like he was too into it and I told him I didn’t want to do that because aside from everything else she is my sister and I just couldn’t do that... well since then things have been weird and I noticed he’s been messaging her on fb and deleting the messages I found the messages the other day I only got half the conversation so I know it was deleted and just earlier I looked and the messages are gone completely..... I’m not sure what to think or even do.... I am sitting by myself thinking everything possible as to why things are going on like this and now I’m regretting even saying anything to him... what would you think feel or do??