Hey plinky,
Jealousy and low self esteem - they're no strangers to me.

Just some friendly outside perspective:

I think it's totally rude if your partner stares at other people for a long time
However, a quick glance once in a while when you see someone attractive may just be a natural reaction; it doesn't mean your partner loves you any less.

I think it's worth having a nice calm talk with your partner about. They probably aren't even aware of how you're feeling. Communication is important in any sort of relationship

Either way, I hope you find the strength to overcome these negative emotions.