YABU, a bit. If he needed to produce a sperm sample with the least possible delay then a wank mag's probably the easiest way. What would he have done without the porn? Used his imagination, I guess. And would whatever he imagined be any more insecure making to you? I would guess not. Unless you think that his jerk-off fantasies would be of your stretchmarks.
Dunno about you, but my sexual thoughts aren't all that wholesome. What's inside his head isn't going to be any "nicer" than what's on the page. Big thing to remember is that it's you he loves.
I never really understand the big anxiety that if your partner looks at porn he's going to be critical about your appearance. Porn is just porn. It's not real. IME, adult men in relationships are highly unlikely to compare their rl DP to the anonymous women in porn. Mind you, I said "adult".
OK, you do get very nasty, violent porn, but I don't think that's what your OH was using. That's a different issue.
I see mainstream porn for men as often performing the same role as romance does for women. Millions of women read slushy fantasies involving other men. Do they compare their own husbands to the wealthy gorgeous heroes in romances? No, the books are just escapist fun. Do their husbands get insecure? Not if they've got any sense.