In my situation, I have only had to deal with her meltdowns and temper tantrums so far. The abandoment fears cloud everything she sees. She has a very regimented outlook on what a relationship should be like and wants SO and I to fit her mold. She asked me what a committed relationship is to me. I started talking in terms of feelings. She stopped me and said "no no, how many times do you want to see him a week?" I told her it would vary upon circumstances. She did not like that. In her mind, there is some invisible line we will cross and become "more committed" than they are.
I will be moving soon and might stay with him for awhile while I am getting an apartment. It's not a big deal to us. For her it is huge deal. She wants to know exactly how long I will stay in his house. We've done this a few months ago when my house was being worked on. She freaked out. She could not handle SO and I having more contact. There is a line again, where if I stay too long we become more committed.
She has issue with a lot of things that we do together. I like to cook for him, we watch tv together and I really don't mind doing his laundry if he needs it, for example. She says these are all "domestic" and an indication that our relationship is too committed.
When I spoke to her, I started out telling her that I was stepping back from my relationship with SO. That seemed to be the only way this was going to work because she had so many issues. She went nuts. She told me, "he's going to blame me and resent me", "I don't want to lose you too" etc. I told her there were consequences to her behavior, the biggest being she was pushing people away.
I think that she is going to lose it again. In fact I know she will. What I need to find out is how SO deals with it. I know I'm not putting up with it. Hopefully he will stand by his word and not cave. This will be the biggest indication to me whether to stay in this relationship.