one former partner is a high school classmate she sees every year at class "get-togethers."

Does he mean, you know, 'class reunions'? As opposed to, oh, literal orgies of nostalgia for the lost times of youth? which he seems to be loading in the subtext?

Anyway, he is being jealous of her high school boyfriend!!!

We wonder whether this is not so much about 'being on terms of friendship with former partners' as actually having had former partners and being on amiable terms. I note we do not hear anything about his track record...