Committed Long Term Relationship and Mistrust

So I know that it is a bit of a taboo topic, but we all know it's a real thing. Porn and masturbation. I have no issues with it. I watch it and do it myself on occasion. But that's when my significant other is unavailable at the time. He didnt really watch it much in the beginning of our relationship. But I just started going to therapy for postpartum which means that for a good few hours I'm actually not home. So I discovered on my first day of therapy he started watching it and it's just become more frequent since. He doesnt know that I know. He does know though, that I do it, the frequency of it, what I watch, and when the last time was that I did. I am very open with him about everything. (Previous relationship that had too many trust issues to count helped) I told him he could be open and honest with me about it and it wouldnt upset me. Which in all reality it wouldnt. But my issue is that he is being very secretive with it and he does it a lot when I am home. I'm readily available and only a room away, but instead he wants to do that by himself. So I guess my question is, is it normal to be upset about the fact he is lying to my face about it and he does it so frequently when I am around? Or is it just my postpartum messing with my mind? (For extra reference and context, I was married to a "porn addict" and an adulterer before this relationship)