MsJam, I can definitely relate. I have six children with my ex husband, and when I divorced him in '93, he didn't call them or see them for over two years. He didn't pay child support either, because he was angry at me for divorcing him and moving the kids to another state. The kids were in so much pain, it tore my heart apart. When my ex actually schedule a half-way meeting point where I'd drop the kids off with him for a visitation period, a couple times he didn't show up. He lives in Chicago and I live in Texas, so half way was Missouri, so the drive back home with kids crying because their dad didn't pick them up was torturing. I just kept trying to reassure them that their dad loves them very much, and is angry that he can't be with them every day and is having trouble separating the anger from the love he feels for them.
Continue to be there for your kids, reassuring them, letting them know they are loved, as you said.
Also.....document everything. I cannot emphasize that enough, but I kept records of everything, including toll tag receipts when I'd take the kids to Missouri. I kept his hatefilled letters, all the correspondence about visitations, every little piece of documentation you need to hang onto. Get yourself a wide 3-ring binder, and I mean WIDE, 'cause you'll need it. Everything I kept came in very handy when my ex tried to have my kids taken away from me on false charges. I had all the documentation/proof that I needed to prove the charges were false, and the judge had a field day with him. I didn't even have a lawyer, since I was providing for six children all on my own income, I couldn't afford a lawyer, and I had to drive to Chicago for the court dates. I was prepared and ready. He went through three different lawyers on each of the three occasions, with each of his lawyers telling him in front of me not to ever call their office again, and one of them even added the point that my ex really screwed up by messing with me in this way.
Document every little thing. You never know what your ex may attempt, neither did I. But, I was ready and you should be too.