If the pic was of a temporary boyfriend and you had sex with him (or your current boyfriend think you had sex with him) you're probably better off without him. I know that's not what you want to hear, but even if you got back together how likely is it that he would bring this up every time you argued?
There's nothing worse than a jealous, possessive, resentful and distrustful boyfriend so my advice is that as painful as this may be now, don't put yourself in this position.
