To those saying they would never walked away... I was one of you and the parental alienation I'm going through has turned my world upside down and caused mental breakdown. It is so easy to say I would never do it until you are faced with the situation and consequences. It drains you emotionally and brings you to the kerb. Suddenly your lovely DC sides up with the other parent and starts hating and despising you. They don't want to know you, don't want to see you again.
I'm in slightly different predicament and I'm a mum, not that it makes any difference. DS is 11, he was forcefully taken of me by exh and I have been fighting in court for residence for last 2 years. For some reason, at the time, the court believed it is in the best interest for DC to live with his abusive father in our family home (I have moved out with DS as exh refused to do it and I couldn't stand the abuse and what he was doing to us).
2 years later, DS absolutely hates me for trying to take him away from his dad, hates me because I have broken our family and destroyed his life - all his words. He has learned how to mentally abuse, control, intimidate others, especially females. He has learned that you don't respect anyone who isn't bigger and stronger. He has learned that he can lash out on me, left me scarred, bruised and say 'you're so annoying you deserved it'. He has learned to enjoy seeing someone suffer, upset and in pain.
It is like he is not my lovely DS any more. I have done what I could have done, engaged and sought help from all possible sources. Still nothing changed. DS is refusing to see me at all at the moment, and he doesn't, despite the court order in place. It isn't so easy and certainly not everyone is able to represent themselves in court. I have already spent thousands on solicitors. Can't afford to do that any more.
As for your DH, I do understand were he is coming from. However, I think he should try to go through the court, he might be entitled to legal aid. Get a legal advice. I would, for my own peace of mind. I would want to know I have used all possible ways to get more, or at least regular contact with DCs. That's what I have done. It still hurts to be in such stressful and difficult situation, but once DC will be older they will also know he has tried and has done what he could have done.
It is difficult to put yourself in your DC's situation. If I was abandoned by my dad and I knew he just let it go and didn't fight for the contact I don't think I would want to have anything to do with him later in the life. If, on the other hand, there was a court order for example and my mum done everything to break it and make our contact and relationship impossible, it still would be difficult, but I would want to give him another chance.
All the very best to you 