What do I do?

My boyfriend and I have been together for about 8 months and I know that doesn’t sound like long, but it feels like I’ve known him my whole life. I love him so much and he has been nothing but kind, honest, and loving. But, I have really bad self esteem issues. I feel so unworthy of him and every time we go out and other girls are around, gorgeous girls, I can’t help but think “why would he want me when that is right in front of him” or “how could he love me when I don’t look like that”. I also notice even the smallest changes in behaviour and lately he seems less interested, less loving, less genuine. I don’t know what to do. I’m so sad because I feel like we’re losing what we had. He’s the best guy I could as for. I know it sounds stupid but he calls me his wife. He used to say he misses me all the time and he used to call me beautiful all the time, but not so much anymore. I feel like it’s ending and I ruined it. Help.