Others have hit the nail on the head. Not that there is ever a time when this is acceptable, but during pregnancy, many men are very protective and more caring while their partner is carrying their child-more so than later possibly.
When he found the SD-ok, he looked at it because he thought it was his. It wasnt. That is when he needed to come to you and say-I found this, Im feeling ......whatever it was he was feeling. He could have ask that you rid of it. You mentioned other children, he knows you have a past-what, who, where, is over-Period.
There are men that would hold onto this, not because they are upset, but because it is their "get out of jail free " card. Something to be used when they get caught in a dirty deed. He cheated. Is this how he handles negative feelings. I am glad you are going to talk to your T about this-you need to be able to say it face to face. Confronting this is asserting yourself. Identifying your feelings (not what you are suppose to feel) but what you actually feel is necessary to protect yourself. Whatever you feel is ok, yet if you are numbing, minimizing, avoiding, ignoring, it will come back to bite you.
I am guessing that with children and one on the way, it would be very scarey to imagine yourself without him, as you feel that he is your rock. You feel that he provides for you in many ways. The truth is something that we do not often see easily, but whatever you feel from his is actually within yourself.
I was in this really great relationship once, except there was something that I was avoiding. I felt safe with him, I felt calm, life was fun, interesting, we had great conversations, etc. Thru therapy, I discovered that those things were all within me, they were all part of me, and I could have them again without him. It was hard to believe at the time, but it was true. I had to face what I was avoiding, he was abusing his clients and he was a therapist.
Please know that I am not criticizing you, you are protecting him more than yourself, making excuses for his bad behavior, and trying to get things back to normal-all at your own expense. I have been there and thankful that I told someone to get another perspective. I have made my mistakes and you are entitle to yours. I just know for myself, and from others posts, that we really want to see you protect yourself before you are put at such a risk that it becomes life changing for you. I knot that I have discovered that finding something out sooner is better than later.
(((hugs)))