In my own experience you have to say you're feeling jealous, insecure and afraid, and maybe angry, too, and have people deal with your feelings. If you don't you're subverting yourself for someone else or just to keep the peace, which won't last.
It takes a long time and sometimes you have to do the same thing over and over again to get it resolved.
With us it was something like, "I'm feeling jealous, insecure and afraid I'll lose you. I'm not asking you to do anything about it, I just need to tell you and have you acknowledge it."
Many talks, many tears and much love later it works out.