Cheating best friend

One of my closest friends of 15 years has been seeing a guy who is in a relationship. He has been with his girlfriend for 10 years and they recently bought a house together.

She has been seeing him for over a year now.

He has mentioned several times to her that he is going to end it with his girlfriend. A year later he tells my friend they are just living together and in separate beds. She has no proof of this. I do not believe this. The guy is still all over and liking her social media pictures. Plus why would he still keep my friend a secret if he was actually single!

I feel so bad for this other woman. She’s out there working hard as a nurse and her boyfriend is being a complete dick (and so is my friend)!

I’ve told my friend how wrong it is. I’ve even distanced my self from her over the past few weeks because I just don’t agree with it. When I see her she is glued to her phone messaging him. I also will not meet him until I know for sure he is single.

How can she be happy sleeping with a guy that goes home to sleep with his girlfriend!

Just to add - I’m in a happy relationship of 10 years. Which is why I think it gets to me so much (she could be doing that to me if I didn’t know her).

There are no kids involved. We are in our late 20’s.

What do y’all think? What more can I say to her? Is it bad I’m distancing myself?

I don’t want to be a bad friend but I’m not ok with it.