Funny you should ask, I was just thinking about this today.
I'm in a long-distance relationship with a guy who's been a friend for many years. I never saw myself as the jealous type (if there is such a type) -- I think I have a pretty... pedestrian view of relationships: If someone really lvoes me, they can be surrounded by runway models with Ph.Ds and stand-up comedy sense of humor, and it's not going to matter. That's how I feel about this guy -- we just fit together on a very fundamental level, I think I am experiencing "grown-up love" for the first time in my life, and I trust him completely and utterly.
HOWEVER -- I've found this fear reaction in myself whenever I see one of his cute students comment on something on facebook... and it's not about him. It's about me. And I know that. I can feel my heart lacing up its spiked sprinter shoes and try to take off and run the other way, and then I tackle it (my heart) and we have this wrestling match where I say, "HEY! WHERE do you think YOU'RE going???" and my heart says "I'm only going to get hurt again and there are so many women in the world who are prettier and smarter and funnier and richer and nicer and better at everything than you are, so I'm going to run like hell right now because I can't take being broken again, OK?"
And then I cradle my heart like I did my kids when they were little, and rock it back to comfort and tell it that we're in this together; we're not going to do anything stupid; and at the first real sign of trouble, we will be running the other way, Michael Johnson-speed. But we need a real sign. Not just brain ghosts that are really leftover toxic gases from a bad marriage to an A.
I have anxiety attacks, too. When I wake up at 2 am and think, "but what if this guy is the same way? What if he's just waiting for me to get comfortable and then he'll start manipulating me and breaking me down step by step?" -- and I think that's, again, something I have to figure out in my head, how to not carry over stuff from the past.