How often do you watch porn in a happy relationship?

I (33F) am feeling a bit concerned about how often my partner (34M) is watching porn and what it means about our relationship.

We have sex, on average, once a day. I know, our record is maybe 10 times in a day (early on in our relationship) and we will go the odd day without due to schedules, being busy or unwell etc, but our baseline is once a day, even when we’ve had rows, because we both don’t like to go to bed angry (to sleep) and so we make an effort to work things through most of the time.

I’ve maybe turned him down for sex under 10 times the duration of our relationship (2.5 years) but I recently found out that he is watching porn almost whenever I am out the house and sometimes when I am in the house (these occasions look potentially revenge/spite when I’ve been too busy to be able to have sex but I’m not sure).

I’m feeling really sad about it, like I’ve somehow failed, because he used to say to me all the time that he was previously always watching porn in his last relationship because they had a dead bedroom and he has a high sex drive, but even 2 years into our relationship he was saying “I can’t remember the last time I watched it” because he just didn’t feel the need to.

I’m feeling heartbroken, insecure, weirdly betrayed and jealous? And yet, I feel like I’m not allowed to be. I feel like if I said this to any man they’d probably just tell me my feelings are invalid, all men do it, I must be doing something wrong, etc. but what can I do if he’s telling me one thing, telling me he’s so happy, that I’m the best he’s ever had, that he loves our sex life, etc. It makes me feel so unwanted that he’s rather do that than have sex with his living breathing girlfriend. Does it mean he’s losing attraction for me?

I’d love to say everything else is great but it almost feels like he’s mentally checking out and that watching porn is also a symptom of this. I feel like we are doomed.