I got really jealous when my ex got a gf 11 years ago. I was naive, even tho I read the Ethical Slut. I thought we were going to have a fun 3some, get together from time to time. It was supposed to be beneficial for me, since I am bi. Instead my ex and the woman fell in love and she wasn't interested in me sexually.
I got SO depressed. I didn't turn to booze, but I was so out of it, unable to function, my ex arranged couples therapy for us with a poly-friendly therapist.
We did couples counseling with her weekly for a year. I also did individual therapy for 3 years. I went on Zoloft for a year and it really helped me have the energy to deal with it all.
The funny thing was, I was always the one to get crushes on other people.
Ultimately, my ex and I separated (after a 30 year relationship/marriage) for various reasons... we grew apart. The woman he'd had as a secondary in 2000 moved in with him 6 months after we split.