Please help 😳

So before my current relationship (almost 2 years together) I had a friends with Benefits we could only sleep with eachother (literally the best sex I've ever had) but we were not together which honestly worked out very well but then I decided I wanted a real relationship I basically dropped him found a amazing man I mean amazing I have 3 kids from a previous relationship (a real one of 7 years that I was extremely faithful in) and he's great with them the man of my dreams but my problem is I can't get this other guy out of my head because the fact we had such amazing sex plus he was a great guy and I've a very very sexual person but my current boyfriend is not and he can't really have sex long and he usually can't go for round 2 😔😔😔 I'm literally so tempted to sleep with this other man and I've never been this way I don't understand what's wrong with me I feel so bad for even having these thoughts has anyone ever had this happen