Hi there, this is my first post so sorry if it's a bit all over! Long time MN creeper, first time poster 
A few weeks ago at DPs family home, FIL was telling us a story about how a young girl still at university who was working part time at his place had almost been sacked and he'd saved her job, being recently promoted to supervisor. We all thought this was really sweet of him as he is seen as lovely big fat caring old bloke.
Fast forward a few weeks, maybe a month or so, and it has come to light that he has been having an AFFAIR with this young girl. He's 56 years old ffs and shes about 19!!!!!! An affair is bad enough but that is just creepy and soooo wrong.
DP kicked off but already within a few days it seems like it's being swept under the rug. I know that it's technically not my family so not my business but I feel really uncomfortable going to their house now, usually we visit at least once a week. I just can't get over what he's done. MIL is so lovely and quiet and sweet and they always seemed like a lovely couple growing old together.
I told DP that I don't feel comfortable going round anymore and that I don't really want to be around his dad if I can help it. He seems upset by this which is obvious and I am being here for him but I just can't face his dad, at least yet. AIBU?