Pics, please. You know the deal.
The only reason your bf would want to meet this dude is to sock him. That would be my thought if I were him, anyway. But there's no way I would put up with this anyway. You'd either stop letting him stay at your place overnight or I'd break up with you. Friends or not, that's an inappropriate situation for a woman with a bf to be in. Sure, if it happened once it was a mistake but for this to happen continuously? Come on now. You're too old to not know better.
And you MAYBE had sex with this dude in high school? Were you really that messed up in high school that you don't remember? You're just burying yourself in this thread. My advice? Post pics. They won't save you, but you'll have some options when this dude finally has enough.