Self esteem.

So I'm a first time mom. Just turned 20. I have a fiance. As we were walking out of church, this pretty girl walks across the parking lot in front of us and I noticed my fiance looking. Now, I know guys are going to check out girls, it's inevitable. Any pointers on not letting it bother me? If I weren't pregnant it wouldn't. But now that I'm getting big (18 weeks) I feel my confidence level on how I look dropping. And that definitely doesn't help. He knows that I saw him because I made a comment on it and how he should just do it when I'm not walking with him hand in hand. We made jokes about it but it still hits on the self esteem