I have the dubious pleasure of being able to see this case from both sides...

My dh has a female climbing buddy that I'm jealous of. She is smart, an ex-colleague of his, funny, charming, 5 yrs younger than me, oh, and I forgot to mention - gorgeous. Guys flock to her like moths to a flame. No, I'm not worried that my dh will do anything wrong, but I'm not happy about the idea that on a sunny afternoon he's out having a terrific time at a climbing crag with this girl - instead of me.

I know my reaction is irrational, and I've stressed it many times to him that it's MY problem, not his, but I asked for one thing - that he invite her home for dinner so that I could get to know her too. And for me it helped just making myself visible to her, if that makes sense. And it helps actually seeing them together, and seeing that they relate to each other on a purely friendly level.

On the other hand, I have a biking buddy who I find very funny and enjoyable to be around, and I noticed my dh looking kind of unhappy when I mentioned going biking with him. I asked dh to come along, but he was afraid of getting dropped...

I then made a point out of getting biking buddy to come inside before the ride to "have something to drink", so dh could see that this is just an average-looking guy, 15 yrs his senior, slightly overweight, who happens to love biking - and not some hot, young athlete...

Point is - jealousy is irrational, but it's also a very painful and humiliating emotion. If you care for your partner you try to lessen his jealousy if you can, without ratifying it.