Why would he say this?

Last weekend we (my boyfriend of 5 years and I) hosted a Friendsgiving at ours and my boyfriend and his best friend got pretty drunk my boyfriend passed out in our bed and as I was helping his friend into our guest room he tells me he has always had a thing for me and that he hopes one day I find out about the times my boyfriend cheated on me and the passed out cold once in the bed. I’ve been debating about asking my boyfriend about what his friend said but I just don’t know. I don’t have any other reason to believe him but this week I just found out that I’m pregnant and I don’t want to get stuck somewhere with someone that has been unfaithful to me. Why do you think his best friend would say that? Should I believe him since “a drunk mind speaks sober thoughts”?

Why would he say this?
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