How am I supposed to feel about this...

So I'm currently 31 weeks and I haven't really felt beautiful about my body lately I have gotten stretch marks I lost my shape so I no longer have the body I used to and I knew that was going to happen but yea so I don't feel pretty at all anymore but my fiance tells me I'm beautiful all the time and how in love he is with me and my body and it always makes me happy but today I had his phone mine was dead and I went on Insta and I'm not going to lie I was snooping beause I am insecure and I do struggle with that in our relationship but I found that he looked up 18+ pages so pictures of girls boobs and butts and those things and it really brought my self esteem a lot lower then it was he doesn't know that I seen it so I talk to him about it and how it made me feel or should I keep it to myself I don't want to argue about it and I know he looks at that stuff we've watched porn together before and stuff but just to give us ideas on what we want to do I'm not insecure about my relationship by any means I'm insecure about myself any advice please