I apologise in advance for this being long and convoluted. I have posted before under other names, piecemeal, some of you may recognise me. I'm indecisive and probably quite cowardly so am probably repeating myself.
I'm on the verge of a breakdown wrt my ex and our acrimonious relationship. Background: we split due to me being pg (he didn't want it), I moved away, came back, we attempted to be friends, ds is now 8yrs.
During those 8yrs his father has been jealous and controlling, intimidating, and verbally abusive. I have only had 2 (disastrous) relationships in all that time. Ex would stop speaking to me if he thought I was seeing anyone. He would also want us to spend 'family' time together and would be affronted and moody if I didn't want to, or if I didn't want to discuss events in my life. (NB ex is in a long-term stable relationship and I have no problem with this, am happy for him.)
A year ago I had enough of all this and cut all but essential contact re handover of ds. Ex had got increasingly moody and unpredictable, he was paranoid I was seeing someone and not telling him, he stopped me doing a sport I had taken up (my first hobby in years) in case I met anyone there ('stopped me' by withdrawing his mutually agreed babysitting role). He also threatened me with calling SS because I 'need a shrink'.
He would also get verbally abusive (still does) if he thinks I am stopping him seeing ds. I never have. In fact I facilitate them seeing each other by doing drop offs and pick ups (ex doesn't drive). The problem is he will text (in aggressive, nasty language) wanting to see ds 'now' and that isn't always convenient. He will also phone up ds and attempt to make arrangements with him. I did try explaining that you might do that with a 12 or 15 yr old, but not with a 6/7/8yr old - you have to go via their mum, like it or not.
Obv this has been hard on ds as he had got used to us being all hanging out. But equally obv he is too young to understand the 'conditions' that faux family time was under. I never wanted us to be acrimonious, I wanted a clean and civilised break, wherein we contact each other like adults but just wrt to timings or handovers and sleepovers. I don't want to spend any time with him, or to see him.
Lately however ex is getting worse. He phones me aggressively, if I can describe it like that. Eg if I don't pick up the phone he will let it ring, and ring, and ring...up to ten minutes at a time. He speaks badly of me to ds, says I am nastly, says I am stopping them seeing each other. He sends me abusive texts (all types of language from accusations of being mentally ill to being a 'c**t'). The last two weeks on pick up he has leaned into my car and shouted at me in front of ds. I have sat there and ignored him. He's a big man, not very bright, very 'physical' and quite scary. He has never hit me but he has a horrible, chauvinistic attitude to women (he thinks this is normal and funny and that he is just being 'real').
Twice I have phoned our local police domestic abuse helpline. The advisor there was v patient and said I should stop facilitating ds's contact with his father on the ground he was abusing me. I said I didn't want to do that because ds loves his dad. She said to change my number and let him take me to court if he wanted access, and to have the police speak to him about the abusive texts and harrassment phonecalls.
I listened and thought about it but didn't want to rock the boat. For one thing going to court would mean ex getting parental responsibility. He doesn't have it atm; if he did he would use it as a weapon. His latest subject to attack me over is because he wants to take ds abroad. I get chest pains just writing that. I know he wouldn't bring him home. Ex is British but his partner is foreign and I know she wants to move back to her home country and for ex to go with her. Ex has also spent a significant amount of time in N. Africa. If I handed over ds to ex with his passport, I honestly believe I'd never see him again.
So...despite my attempts to keep quiet, keep my head down, roll with the punches etc, things are getting worse. Ex texts me every day, if it's not aggressive, vulgar abuse it's stuff like "All this is your fault," "DS is suffering", "We could sort this out but you don't want to."
DS is regularly tearful over this. I'm not well. I can't sleep for worrying what will happen next. DS comes home and says stuff his dad has said about me and it's agony, it's so not true. I've always wanted him to have a close and loving relationship with his father. But his father is such an awful, awful man. And he's ds's only male role model
I am living hundreds of miles away from family, I have no friends really, certainly no male friends. No-one to help or stick up for me or even to talk to. And as the days go by they are turning into months and then it's be years and before I know it ds will have turned into a mini-me of his father and will despise me for things I haven't even done and will likely to go on to treat women in the way his father does (he has been abusive to all his exes - he admits this - the woman he is with now is young and very naive, prob has it all to come). I am noticably touchy after encounters with ex and ds is suffering. He sometimes seems wary of me. I know this is because I snap, when I am thinking of ex being horrible to me, and how much I'm totally stuck and confounded, I get irritable and shouty. I know it's not good and I'm trying to control it.
I'm increasingly distraught by this. Anyway if you've read all this thanks so much for perservering. My dilemma is basically, do I just run, start my life over? I have a very small amount of family a very long way away, we are not very close but they are good people and I know they would help me as much as they could. This of course would mean moving ds away from his father and that side of his family (ex is mean and horrible but the rest of them are lovely and ds sees them a lot). So, probably, ds would end up hating me anyway: if not because his dad has taught him to, because he will remember being moved away from a father he adores. (As well as a town he has lived all his life in, school he's attended since nursery, etc.)
Of course I have no idea how ex will react. I have heard through reading on MN that he could trace me via child benefit. So he could still take me to court anyway.
I am not rich, I have no career, I earn a low wage working PT and would have to rely on staying with family in the short term. This is not ideal, I love where I live now, family don't stay in a nice place.
Even to contemplate this I would have to borrow the 8yrs-worth of savings in DS's name (his gifts from relatives over the years, plus a bit from me when I was better off) and never touched before. I feel like I'd be robbing him.
I'd always be looking over my shoulder 
DS would miss out on the good aspects of having a father around. I always wanted for their relationship to be a separate entity to my relationship with ex. I am constantly telling ds how much his dad loves him and loves spending time with him. Admittedly I'm struggling to find virtues to extol, without wanting to be vicious ex is not a good father. He doesn't have the same moral code as me, he is a 'lazy' parent, he's fickle (took off to live abroad for 2yrs of ds's life), questionable ideas about taking care of his safety etc. But ds loves him, they have a laugh together.
WWYD? Don't hold back on any emotional or legal realities! And apologies for anyone who recognises me. I think I post about this on a six-monthly basis under one name or another. I asked one RL person about this some time ago and she sympathised with ex, in her opinion there is nothing a father can do to the mother that warrants her deliberately moving away to escape him. (Well maybe if he was violent she might mitigate that thought, but he has never physically abused me.)
I am thinking of going to my local women's aid for a chat about this but because I am not in acute crisis I don't want to take more of their time than is necessary, hence asking for opinions from MN.
TIA. As lots of you who are isolated in RL know even one or two words of understanding really mean the world.