Maybe try asking your bf to close the relationship first. You tried it, it didn't work out.

After that you just have to tell him what you've written here. It was a mistake, you regret it but this is how you are feeling now.

The big problem, as I see it, is that you are putting the ball in his court to make you feel more desired now. He should have been doing it as a matter of course through normal aftercare (and I'd explain this to him) but at this point it's going to sound a lot like asking him to do all the work to mend the relationship. Maybe he's fine with that, in which case I'd say you have a keeper, otherwise you might be in trouble as a couple.