You seem to be in the same situation as I. My ex lives 3 hours away and on paper has liberal visitation with the children, yet he has chosen not to take it for over 2 1/2 yrs with our kids, 13yr old boy and 15 yr old girl. He started out 7 yrs ago seeing them, when either I, his sister or mother picked them up and dropped them off. Then he started skipping visits, after talking to the kids on the phone and saying he'd be there. One time he was flying into town from seeing a girlfriend in Alaska at 530 am so the kids were up and packed and waited 3 hrs and he didn't bother to call to say that he wasn't coming, though from the airport less than 2miles from our home it was a local call and would have been the right thing to do. Took us 3 days to figure out what had happened and if he was alright. The kids were worried he never made it to the plane, the plane crashed, something and rightfully so. Bawling 7 and 9 yr old children are no fun and scares the hell out of a parent, knowing someone else is causing this pain, someone who made them and is supposed to put them first.
I was married to my ex for 10 years, separated another 2 and in that time I learned how vindictive he could be. I put the kids into counseling so they understood that it wasn't their problem but HIS. I reassured them that he loved them, just not the way we wanted him to show it, like taking his visitation time with them, calling, sending birthday or Christmas cards, etc. Now the kids are older and truly want nothing to do with him whatsoever. It is a sad place for them but I try to keep them from truly hating him. Their hearts are closed off to him right now. Maybe when they are adults they can confront him, though we've been told that he won't contact them because of me. He promised me when I left that he would make me pay for leaving, through the kids. It took a few years but he has done it. But in the end it is he that suffers and the kids don't ask about him at all. We have his phone number finally but they refuse to use it as the last call that was placed was when my 15 yr old was missing for 40hrs and his girlfriend called to see if "THEY" could do anything. He didn't even have the nerve to ask me himself. Sad. When my daughter found out his gf called, she was mad and refused to call him back, and I feel rightfully so. I told her it was her choice and she says she refuses to speak to his gf who has 5 kids of her own.
I know what you are going through and the pain your kids are experiencing. I found that I truly had to stop expecting anything from him, as other moms have posted here, and then we weren't disappointed and the kids weren't left feeling hurt by his inactions.
Try some counseling for them, one on one if you can. They need to get their feelings out and be reassured that it isn't them, it is his choice to live his life the way he wants.
My husband has taken on the role of dad with the kids and takes them places that my ex should. We have 5 kids between us, my two, his 17 yr old son (we are custodial), his 8 yr old daughter who lives a mile from us, and our 5 yr old son. My husband tries to do things with all the kids individiually. It might not be every week since he has a very demanding job and doing something with each kid would take 5 nights a week, but he does try to take them for a day every month and spend one on one time with them. When his daughter is here most of the time he takes the 2 youngest somewhere together so they can play.
Your boyfriend sounds really understanding and wants what my husband wants from my ex too, but as we have learned, with my ex, and his ex wife, we cannot make them be good parents.
I hope you have a good visitation schedule set up, and I learned to follow that, not allow my ex whenever he wanted if he just happened to show up in town (though he did deliveries here in town every day of the week for over a year, he never called his kids once during that time). I never ask anything of my ex that is outside the scope of the agreement or financially. I just don't rely on him. He is incapable of giving the kids what they need or putting them before himself.
We are revising the parenting plan since in OR if the parent does not have contact for a year with the child/ren, that is considered abandonment and grounds for parenting time to be cancelled. I've given him almost 3 years to fix this and I won't have him giving the kids false hope any longer.
Good luck to you. It is always hard on us when we split up and we don't want our children to suffer, but some men just can't seem to cope with the loss either, even if it's what they want and children are a reminder to them that they failed as a husband and father. (At least that's the perspective many GOOD dads still involved have given me as a reason why a father would abandon their child, and also the psychologists we've seen).
Lots of hugs to you. Stop calling him and let him be. If he knows when he's to have the kids, well, that's his problem. If you need to call to see if he is taking the kids on his time, do so but give him a day to call by to confirm. If he doesn't then keep track on a calendar, etc of the times you have tried to foster the relationship between the children and their father. If he doesn't call by that day, then make your own plans and don't let him disrupt them. Keeping track of things is very helpful later on, especially if he is vindictive and states you haven't worked with "his" needs and schedule changes. Make a simple call before an upcoming visitation time, state he needs to give you an answer by X date and stick to it. No answer means no visitation. Do this for a few months and don't discuss anything else with him. It's hard, but chasing him down will make him more spiteful and incapable of giving what the kids truly need. He needs to do this on his own.
Lots of hugs. So been there done that. :-)