I think she should end it but she can also choose to add to his shame by dumping him on Facebook too if she wants. I don't consider him to be worth a phone call so if OP just changed her Facebook status, that would be fine too. OP's choice.

Or do the same about his cheating as his mom did about the sex

I'll probably get some thumbs down for this, but depending on OP's relationship with her bf's mum I'd call up to confront him about it, and then end it if it seems obvious that he's cheating. Some assholes are capable of that sort of betrayal, but some asshole parents are also just as capable of hating their child's relationship/significant other so much that they would make up a cheating story to make them break up. It'd be terrible if OP's bf is experiencing this situation: Today, my mum hated my girlfriend so much she posted a fake story about me having another girl in my bed on facebook. Now my girlfriend won't talk to me. FML. Talk to him and get his side, then decide if you trust him or not before walking away. You'd want the same if it was you.

yes. just like I only want nutella :)

yeah good luck trying to find loyal man...ha ha ha!

I don't think there's any pleasant way to find out..

If you say so... ( ͡° ͜ʖ ͡° )

Sorry, what?

*Proof that there will always be assholes

Sean Connery is sooo fine...anyone remember that movie First Knight with him and Richard Gere??? Great movie...

Sorry, but the cheat is embarrassed enough already. Mum did the right thing.

If everyone found it funny, I don't think they realised he was cheating on OP.