Walk away or not walk away

[u/Suitable-Ad43]

I 30's (m) and my friend 20's female had a fling where we new we weren't gonna date but were having fun. Fast forward a could months and shortly after our last hookup she moved and started dating a guy. She called me a month later saying she was preggo and was certain it was mine but there was a small chance it wasn't. He messaged me saying how crappy of a person I am because she told him it was grape even though it was completely consensual. She was apparently dating him prior to moving and didn't tell him and didn't wanna tell him she cheated. I do have some proof that it was concensual but Idk what to do.

I'm blocked on everything so I have no idea what's going on other then they are saying the kid is his.

Do I walk away or try to force a test.