Nelli good luck. This all struck a cord (EX Major I think) because I've been to hell and back with my DP's ex.
She has a few more issues than the usual - if she doesn't keep in touch with DP and her DD ALL the time she believes that something terrible will happen ie they will die and that its only by constantly being in touch that she can cope with the terrible anxiety that causes her.
She also hadn't let go of the relationship - out of habit or preference she still seemed to prefer turning to my partner over her own, and was threatened by me because she hadn't ever thought about the reality of her ex ever taking up with someone else. The reality, along with something of a guilt trip at the way she ended their relationship left her going full pelt for BM of the year award inside both her, and our, relationship, hit her very hard......which meant it also hit me.
I ended up seeing a counsellor because like you I was going through the roof every time she called(and boy did she call). I learned to recognise that much of it was down to her issues not me which I shouldn't take responsibility for. I found ways to not absorb her issues like a sponge but to put up mental walls that kept her out of my head. The stress I was feeling was a natural response because she was imposing her needs and issues on to us.
Each of us have boundaries when it comes to what we can cope with when dealing wth others and when they are crossed (especially if you have no control over it) you will get stressed and knotted up. There's nothing wrong in feeling like that.
I learnt that while she is a part of our lives she doesn't have the right to impose herself, she was still grieving for that relationship but that didn't mean we all had to wallow in it, and we have the right to have some uninterrupted private time with each other where the past wasn't allowed to go. Your DH can help in this if he refuses to discuss the past with her, its not saying it means any less to either of them but insist it stays where it belongs - it takes two people to have a conversation. Its not just about sorting out your feelings, its about renegotiating the boundaries of your relationship with her and your partner so you can all live with the situation. You have the right to say to your partner and her that you am not comfortable with her bring her emotional issues and their past relationship to your partner to deal with. She may not like it, DP's ex hated it and me for suggesting it might not be appropriate behaviour - but she stopped, and is getting herself some help, my DP came along to counselling with me and discovered a few ways he could help both of us to - some of it was down to him as much as her because he hadn't made the boundaries clear to her so she thought it was ok, and I'm still here and (mostly)sane
In my case we talked around it and ended up with a shared online diary so everyone can add all the little details to it such as picking up times or lost socks. That way we save talking for the big issues and texts for emergencies. My partner keeps the talking to practicalities rather than allowing it to drift to social stuff (and crying on his shoulder is out, he made it clear that's what her new partner is there for) - and that if he needed to talk over something to do with the children with her that affected me too I would be included in the conversation. She still calls more often than I'd like when she's feeling low but mostly from 30+ 'boundary violations' a day we are down to a manageable couple of conversations a week about practical stuff and my stomach muscles are slowly relaxing.
There's no right and wrong about this you have to work out what is ok for everyone - including you.
Bad guys of the world unite (you have nothing to lose but your relationship, sanity, self esteem etc)
issy x