How can I lessen jealousy and paranoia over my partner checking out other women?

I go to the gym most days with my partner.

I don’t want to stop going with him as it works perfectly for our shared routine, but I am finding it a frequent source of anxiety when there are women just wearing booty shorts and a skimpy sports bra.

It’s like I go on high alert and I can’t stop myself from using the mirrors to see if he’s looking at them if they’re working out near him. Sadly, he often is, and it makes me feel weird as hell.

I have struggled with my body image my whole life, from being very overweight to being anorexic and underweight.

I am currently feeling mostly okay, lifting has helped me recomp my body and I have a better ass/thighs than I ever have…but I still dress quite conservatively to hide what I’m uncomfortable with.

I have no animosity towards these girls, they have beautiful bodies and it’s their right to wear whatever they like. I am conventionally very pretty, but about 5kg overweight.

But when I catch my partner looking, my stomach plummets. It starts an avalanche of negative self thought, something I have had a problem with for a long time. It’s like another voice comes into my head and says the meanest most defeating things. Most of the women are much younger than me (33) and it also activates my fears about him finding me attractive as I age.

I understand we’re all animals and that it’s normal, it’s not like I don’t appreciate the male bodies in the gym. I have expressed my worries and how it makes me feel and the upshot of the conversations is usually that he’s sorry that it affects me so much but that he finds my jealousy exhausting and controlling.

I don’t want to be like this, but it happens so quickly and I feel like I’m taking psychic damage sometimes.

How do I come back from my thoughts and get some perspective?