My boyfriends ex wife wont let him see his kids and it's starting to affect our relationship.

First off, I'll start by saying that my relationship with my boyfriend is amazing. He's very caring and does a lot for me and my 4 year old daughter from my previous marriage. We are truly best friends and talk about marriage all the time. I'm 27 and he's 39. I love him more then anyone I've ever been with. He's (in my eyes) everything I've ever wanted in a mate and husband. He's smart, successful, funny, caring, providing etc... We've been in a relationship for 6 months but I have known him for about a year and a half and he's always been a wonderful guy.
His ex wife left him about two and a half years ago and has been making his life hell in regards to his freedom(she's gotten him locked up numerous times falsely) and the two children they have together. She's gotten a restraining order on him so he cannot see his children or contact her but she has been texting him and calling him even though she has this restraining order against him. In the texts she says she wants him to respond because she wants him to go to jail. Of course his lawyer has told him under no circumstance is he to answer her back and he hasn't. When he first told me what was going on, I was doubtful of what he was telling me because there is always two sides to every story. Until I saw what was happening with my own two eyes. I have seen her text him stupid things like she's gonna make sure he's broke forever, he'll never see his kids again, she cant wait for him to fail in life, and things like that. She even finds the stupidest reason to text him like saying she's going on a vacation in April of 2016 and needs him to watch the kids that week.. That's almost a whole year from now! But you get the point. Three months into our relationship he introduced me to his children. They are very sweet and we all had a blast hanging out together. Once the children returned home to their mother, of course they told her they met daddy's girlfriend. Since then, things have intensified a bit. She texted him saying the kids like me and they need to call me Miss (stupid and petty in my opinion but they are her children and I'm not going to get in the way of her parenting.) Of course my boyfriend cant respond due to the restraining order. But we started to see things change. She started letting him see his children more and we thought that was great. But one of his friends put this idea in my head. The only reason why she's letting him see his kids more is because she know's that he wont have much time to be around me because for the most part, when he has his children he does things alone with them which is perfectly fine with me because we've only been together for 6 months and I'm sure it must be difficult for the children to see their dad with another woman even though as I said, when we did meet we had a blast. He has a little girl who is 10 and a boy who is 7. She has texted him things like, the kids don't want to be around me or my daughter. The children and my daughter have met once and had a great time together even though my daughter is a bit younger then them(she's 4).
About 2 months ago, the ex wife texted him and asked him if he could watch the kids for a week and pick them up from school. His mom responded for him since he isn't supposed to have contact with her or the kids, and said of course he would watch them for the week. Once they went back home to her, she got into an argument with his mom because his mother wants to know why she keeps harassing her son and why wont she drop the restraining order if she needs him to sometimes watch the children. All hell broke loose. The ex wife then said that he could no longer see his children and has stuck to this promise. He hasn't seen his children for two months now and it's been making him very depressed. To the point where he doesn't really see me that much anymore (MAYBE twice a week) because he says he's depressed. I don't want to seem like I don't understand that because I can see why he would be depressed about that. But it's killing me. I've talked to him about it and he says I don't know how he feels because I have my daughter everyday. I'm trying to be sensitive about it but I have needs too. And I know if I was depressed I would want to be around him even more because he makes me so happy but he says he just needs to be alone when he's depressed. He used to be very happy and fun but now he's turning into a shell of a person because he's so depressed. He just stays in his bed all day. We talk on the phone a lot through out the day but it's not good enough for me. I want to be with him. Hug him. Kiss him. Try to make him feel better by doing nice things for him but he's not having it. He has some good days but for the most part he's very upset. I love him so much and I don't want to leave him but it's killing me that he's like this now. And it's killing me that his ex has this type of control over him to make him so depressed and use his kids as pawns. I've told him to go to court and show them the texts she's been sending and try to get the restraining order removed and possibly get joint custody of his kids so he doesn't have to worry about what makes his ex wife happy just so she wont keep the kids away from him, but it just seems like he's too depressed and tired to do anything like that. I know you have to stick by your partner through hard times but I'm feeling neglected. Alone. He still tells me he loves me so much and he's going to marry me all the time. What should I do? I've told him this is killing me too now and I feel lonely and he says "Sorry, but this is how I get when I'm depressed." Should I cut him off and give him time to get this situation fixed with his ex wife? Or should I just ride out the storm with him?