How about I invite my friend to my flat even though he cheated on my flat mate?
I hope this is a big joke. Why would you still invite him over?
I don't think it's a big deal.
If you know that your friend cheated on your flat mate, why do you think it could be okay to invite him over? It's not right to make your flat mate uncomfortable intentionally.
Maybe I just want some male company over. Maybe she will learn a thing or two about her boyfriend.
This is not going to go well. I don't think this should be done, things will get bitter between you and your friend who was cheated on. Do you want for that to happen?