If my boyfriend is with someone I don't like our lives are living hell until they are no longer an item.
If he's with someone I DO like I don't generally have a problem. I'll have the general security issues but once I meet the person and discover I do like them that usually goes away.
Just this past week we've been dealing with my insecurities, and they are HUGE insecurities, dealing with a relationship that ended with me several months ago. It effectively ended with him Thursday but in actuality it ended shortly after it ended with me
It ain't easy dealing when you don't like the partners, that's for sure.
I don't really know how I do it other than talking A LOT to your partner. I tell him how I'm feeling without saying that he's making me feel that way.
I know there are others who deal with this a lot--they don't like their partner's partner.
When he was with the one lady I had to be doing something else during their time together other wise I was totally miserable.