PA? MLC? Please shed a light

[pickled]

I'm new- I'm not sure if I'm posting right-
My H & I have been married 10 yrs. We've had an incredible bond that has gotten us through some really rough times. 4 years into our marriage H had surgery that led to chronic neck pain, and then 2yrs ago to pain med. addiction. I thought it would be the most awful thing I would go through. I was lied to & betrayed. He spent 3mo in rehab. I stood by him, went to C & we repaired the damage (to ourselves & our M). He's been clean since. We decided to have kids. I found out I wasn't able to get pregnant. We were strong, decided to do IVF. It failed. It was a horrible disappointment. We decided to take a break from the baby thing. We had our 10yr anniv. had an amazing vacation & talked about how far we'd come, all we'd gotten through, and how we were at the best place we'd ever been. That was in May. In June, things started to change. He started excercising alot (late at night), becoming distant, and not wanting sex. He said he was the most in touch w/himself & he hadn't felt better. Started blaming me for some of my traits.
H found out his dad was really sick-flew back east to see him. He came home not missing me (very out of character). He stayed out late all week, then went on a trip w/some guy friends. Again, came home, very distant. I started to talk about things & he'd say he's doing what he needs to do. I got suspicious. I found out about a "friend" he was calling alot, late at night. I confronted him with having an affair. He said it was innocent, & he'd kept his friendship from me because he knew I didn't like her. We argued, then let it sit. A week later I had this gut feeling to go by her work. His car was there. He came out 2 1/2 hrs later. I asked later where he'd been-he lied, and I busted him. We argued, H said she was just like any of his guy friends, and that he wouldn't end the friendship. Started saying things about the uncertainty of our R, and that she has nothing to do with our problems. He left again to help his dad, who's dying. He lied to me about where he stayed the night before he left. I don't know what to do. I'm angry, lost, and confused. I want to know if H is having a PA. I don't know if I can go through rebuilding a M again if he's having a PA. Should I contact OW husband? I need answers. Please shed some light.
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ME 31, H 40
M 10
NO KIDS
MLC? PA?