Suspected Cheating- do I have a good start? and how can I catch him!?!?!?

Well nothing in your post infers he's having an affair. It sounds as if you we're suspicious well before she entered his life and she's become your new focus (primarily because she's a focus in his life). I really don't see anything other than your umption that the pregnant woman and woman who plays drums are the same person. Which doesn't seem like something of which you have actual confirmation . My question would be, what's your personality type? Are you a bit jealous or have been told your a bit jealous or a little contolling? Sometimes we can get the best of ourselves in life. I'd maybe look for more solid proof before venturing down that road. I'd talk to him about the how the situation makes you feel uncomfortable and that you need some help resolving this issue. As to his time spent with you and your children accept nothing, but his presence on these family trips. Speaking to the weekend work issues ask him to arrange to complete this either at home or during the week, so as not to interfere with family time.