This is a great question.
I have the same question( except the marriage part-but we've dated for almost 6 yrs now, and have a planned 7 month old baby).
It hurts me, also. For me, it's also a trust thing. You feel like you don't want to leave the house ever. It makes me feel very trapped and stressed.
I don't mind him looking at it once in a while, but I'd rather he looked at it when I was around and included me in stuff like, " Oh hey.. look at THIS! teehee" or whatever.
Good luck. I've talked to my boyfriend about this, and he just doesn't get it.
I'm glad there are others out there that feel the same way. My boyfriend has slowed down considerably, and hides his tracks much better, now, but it doesn't stop the fact that I don't trust him while I'm gone.