Lucybabs,
The sex is really incidental to your question...
But to get to the point, no I don't feel jealous about DP loving someone else (or having sex with someone else).
I think it comes down to your understanding if love. I don't think that love is a finite entity - in that if DP also loves someone else that must mean he loves me less, because there's only so much love to go around.
Like when you have a second child you don't suddenly love your first child half as much...
But jealousy is about thinking someone has something you don't have and that you want.
I know DP loves us both, differently but equally. And there are very few aspects of their relationship which would fall under the category of "things she has which I don't have and wish I did".
And it's funny, actually, if something crops up which gets me feeling that, when I look at all the other things which come with it, as part of the package, then suddenly I don't want it quite so much!
I can't say I never feel it (I'm human) but on the very rare occasions I do I feel it, and if I it's usually pretty easily dealt with by looking hard at what you're actually jealous of, and why.
But in short, I'm not disadvantaged in any way by DPs other relationship. Quite the opposite. I don't wish I had their relationship, I like the one I have with DP. I don't think it means DP loves me less. So what's to be jealous of?
To be honest the main challenge is not jealousy, it's diary management. We have a shared google calendar which has to take into account the needs of three adults, two households, two teenagers and two small children. And sometimes the complexity of that does my head in!
All those who think poly is just a giant fuckfest is underestimating the amount of time devoted to huddling around a calendar.

