How do I stop valuing physical attractiveness so much?

I don't like my self image because I've always been 5-15 kg more than I'd like to be and I have never been able to get rid of them. I also have a happy relationship and I think my boyfriend has an attractive body, although he isn't fit per se he isn't bad physically, at least not as much as I see myself, so its never been an issue.

However my self esteem is poor, and whenever someone physically "superior" than me is flirty with me I feel like they are validating me and it makes me play along which hurts me and my relationship. I think part of this stems because while I have been with a bunch of people none of them were particularly fit so a part of me wonders what it's like and another part of me wishes I could be like that. When I see someone as fit as me or worse I see them as people, but whenever they are more attractive I see them as something else.

On the other hand I've never had an issue with my body in front of my boyfriend, but I guess since he isn't very different from me physically it doesn't feed this bad psychological need.

The catch is, I don't really care about these people. I don't have any feelings for them, but I can't stop thinking about how hard it is to be in shape and how they make me feel good and it makes me feel sad because I want to be better than this for my boyfriend.

Please, help me find a way to fix this issue. I don't know whether I should focus on seeing these people for what they are, just people in better shape and no different than me whatsoever, and get over it, or focus on my low self esteem. I don't know if anybody else has this problem but it would be nice to hear similar stories.