Okay - I should add more. I have been feeling very left out since this woman came into my husbands company. She came in the very month I gave birth to our 1st daughter. We went on a compnay trip to Mexico and she was there. I felt the chemistry between them instantly and my gut instinct kicked in. Since coming home from Mexico I have found our cell phone bills which show many many calls at weird times as well as when they are both supposed to be with their families. Oh - my H said that the cell phone company made a mistake!!>> Whatever!!! Then, about a month ago I found a text message from him to her saying, "I miss you baby". when I confronted him about this he said it was an inside joke.
He says they are friends. Yet he knows everything about her bad marriage and he tells me that she knows nothing of ours.
What should I think?? Do I believe him?? HELP!!

OK, red flags, red flags all over the place.

Trust your gut feelings:

You detected the "chemistry". You found the incriminating cell records. He "knows" all about her "bad marriage".

This all screams "affair"; if not PA, then at least EA, which is only steps away from a PA.

Do not believe him. No H says "I miss you, baby" innocently to an ow.

Oh, and the phone company does not make this "kind" of mistake.

Do more digging. Do not divulge your source. He will only get more sneaky. Is the ow still with her H? When you have what you feel is enough "evidence", expose to her H. Do not tell your H you are going to do this; just do it. She may be lying to your H about the state of her marriage.

Good luck.