Why does my (26F)boyfriend's (29M) behaviour change when he watches porn?

My (26y F) boyfriend (29y M) have been together for almost 2 years now. He disclosed to me that he has had a porn addiction growing up but he has worked on it and is not watching porn as much he used to back in the day. However, he did confess that he does watch porn occasionally (I'm not sure of the frequency). Im not upset with this because he said he is working on stopping altogether and I trust him on this.

I notice, however, that every time he does watch porn, his behaviours towards me and our relationship changes slightly. I notice that he becomes less affectionate, doesn't say "I love you" often (he usually says this all the time), doesn't say i love you back when I say "I love you" first (he always does this too), seems guarded, doesn't maintain much eye contact, his smile fades slightly and doesn't seem genuine and doesn't interact with me much even when I initiate (which makes me feel ignored). It makes me feel like shit.

I have had a conversation with him about the fact that he changes but didn't have much info to share with him in regards to how exactly he changes. I only recently figured what exactly changes in his behaviours and I am planning to have a conversation with him about this.

Has anyone else experienced this sort of change with their partners and any idea why this could be happening and what we could do ?