How to improve self esteem in relationship?

I'm in serious relationship. I completely trust her and she's a very good girl. A lot of guys tried to chace her and I know she chose me over other guys.

But still, when other good looking guys (I'm not bad lol) try to contact her or approach her, I feel discomfort and jealous.

She rejects them right away. But still..
What should I do?
How to improve self esteem in relationship?
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