I’m so insecure..

I’ve started seeing a new guy. He’s only the 2nd man I’ve ever been with, and I have kids with my ex husband. I’m so insecure about my tummy. It has stretch marks and loose skin. It hangs from having a c section but I’m not a big girl. I know it looks funny and I hate it but I’ve tried not to let it bother me. Yesterday, we were taking pictures together and I saw pictures of another girl in his phone. She was shirtless but covering her nipples. She was tiny and beautiful. She works at a bar that we frequent together. He has a high body count but I’m the first girl that he’s ever dated (he’s 24). I can’t shake these insecurities. What do you all do to feel secure?