I would ask not to be told how often my partners have sex - it's not my business and if its hurting you and not something you find sexy, then ask for it to not be mentioned again. Not that you wont know they are having sex, but why would you want reasons to be unhappy, to have the subject come up in a way that is stressing you each time?
The only solution that I can come up with is to decide what you need in the relationship to be happy (sex every X often, dates every X often, feeling heard by your partner, etc) and see if you are getting that, and if not, work towards it, and if your partners arent willing to work towards that or let you know they can't provide it, then the relationship probably is going to be a source of stress for as long as you let it feel that way.
I know I'd be unhappy if my partner who I'd like to have more sex with started having lots of sex with somebody else, so I'll make sure I never ask about frequency, though I would ask if it was awesome (and hope it was). Comparison is just a bad thing, never useful in dating or love.
Happiness will never come to those who fail to appreciate what they already have.