I wouldn't let my kid near him with a 100000000000 foot pole. I don't care if he's her father.. lots of men can be fathers.. but then again.. a lot of them suck!
I was lucky and have a fabulous father, but a lot of my girlfriends have crappy fathers and they are still to this day dealing with the pain and crap as a result of it.
That girl should NOT be in bed with him and his gf.. especially considering you aren't even divorced or legally seperated yet. Call a lawyer tomorrow and tell them about this. Also.. talk to kayleigh about it and see who she thinks this new girl really is?