This is easy................bin him. If he needs a sexual release he should be coming to you or dealing with it by himself if you get my drift. I work away for half the year from my wife. I work on a dive boat for 5 weeks and am at home for 5 weeks so I do alot of "dealing with it by myself" at work. I don't go jumping into bed with the first woman I see when my ship gets into port. Bearing in mind I don't look for it anyway. Did all that when I was single. Simple sailors demand simple things - cold beer!
It's taken my wife a long time to understand this, that I'm not messing around as soon as I leave the house to go to work but now she realises how strong my love for her is. So we have the all important trust.
If a boyfriend / girlfriend has cheated with who ever there is no reason why they won't do it again no matter what they say. Cut and run, it saves time and hurt in the future.