Venting and advice needed

Hi all - in a situation that I'm struggling to handle and seem some perspective and some advice if anyone has any!

I am in a relationship with a man with kids, knew beforehand, not an issue, in fact im dying to meet them. We have been together since July last year so approaching 12 months together soon, and it has been a massive struggle.

The last 10 or so months have been constant up and down thanks to his ex. There were months on end of her sending him abusive texts threatening for him to not see his kids if she didn't get her way. There was one incident where we had changed around when we would see eachother (we only see each other once or twice a week as it is) so that she could go on a date with someone she was seeing, on the provision we would get a weekend day together a few weeks later (he has them the one weekend day he has off unless a miracle happens so we tend to see eachother in the week where I have to be up at 5.45 and out by 6.30 to 7 o clock) and when that day came around she wanted to go on a date with someone else to spite who she was seeing and told him he wouldn't be seeing his kids if he wouldn't change his plans last minute to suit her.

She's even sent me an abusive message before accusing me of trying to make him put me first and not the kids. He had to go and collect something from hers before we drove for a weekend to see his family once and she told him that because he had debated me being in the car (outside, no where near the house or kids) he wouldn't see the kids on his birthday on the Sunday. Sunday rolls around and she lets the kids call asking why he doesn't want to see them on his birthday.

It just never seems to get any easier, I pretty much get told when I'm going to see him by her choosing when she wants to see her boyfriend. He doesn't really have any interest in being involved with the kids, which is primarily why I'm not allowed to meet them as well as the fact that she does not like me. My OH is too worried to ever say no he can't do a certain day or ask if he and I can spend a certain day together it's always a flat out no. He's a very flexible involved dad - does school runs in the morning so she can go to work early or the gym, picks them up from school the days he finishes work on time, he's always the one to leave work and head to the school if his son (diabetic) needs anything even though her work is much closer, very accommodating for her when she asks/tells.

I also most weeks don't know until the Sunday when I will be seeing him the following week even though she works the same hours every week and he gets his rotas done 3 weeks in advance - she just refuses to plan ahead. It seems a little unfair (this is where I probably begin to sound selfish) that it always seems to be OH and I trying to squeeze in time together so they can see eachother when they like. He works a minimum of four nights each week, sometimes five, until 10 or 11pm so it's not like I can spend quality time together every night he doesn't have the kids.

She's quite happy to plan holidays with her boyfriend in advance and demand he books the time off of work, but can't plan a week or two in advance when she wants him to have the kids to make everyone's lives easier. The cynic in me says she deliberately does it so we struggle to make plans, she's never been supportive of his relationship with me. It also looks like we may struggle to go away anywhere this year if all of his holiday is used to accomodate her going away, so possibly it'll be she's gone away 3 or 4 times and we won't have gone anywhere. It all just seems highly unbalanced.

I just feel that nearly a year in, when we will end up living together soon, we should be in a position where I have met the children. She's making life more difficult for herself by not allowing it, as we'd be able to have them more together than he does alone. She has said before he shouldn't have to rely on her telling him when he has the kids to which he replied that she says no when he tries to arrange otherwise, and he wants to have a relationship and is happy to have the kids more, but with us having them together. She did say a while ago that when we move in together we could be introduced, but who knows when that will be.

It just puts a lot of strain on our relationship. He has said that I will meet the kids regardless eventually, but I don't know what it will take for him to actually turn around and say that I am meeting them and she should accept it. His daughter has asked many many times when she is going to be meeting me. We end up arguing quite often because I get stressed having to plan my week last minute because I don't know when I'm going to be seeing him, or just stressed in general because I didn't think we would still be struggling this much for me to see the kids a year down the line.

I know this is a long post, and I know the priority here is the kids, I quite often get called selfish by him as I want to talk about how it all makes me feel, but I don't have a massive amount of friends, and the people I live with are people he works with so I don't want to drag them into any stress I have so unfortunately unless I bottle it up, he is the person I talk to, which doesn't go well when it's the same thing I'm saying over and over.

I guess I just came on as we had a disagreement yesterday and it just feels like too much today. I know that once things are all settled that we'll have a wonderful life, I just kind of thought it would be more settled than it is by now. He made a comment this morning that his only frustrations lie with me right now as she is being okay with him, which all I could think is well of course she's okay she's in control of the entire situation, including some of my life to an extent. It's just all very stressful and I don't know how to manage it better...