Being serious though, you need to talk- is he deciding to do a vasectomy then backing out last minute, but after planning to do so, or when he says he'll do it (each year), is he aware he won't do it and is saying it to make his life easier?
Urgh, he would have lost all my respect with his actions, I would tell him so and would not be having a sexual relationship with him anymore. All pressure would be off, he would not have sex until he had the snip, plain and simple. After six months I would book myself in for a vasectomy, inform him when that would be and that he would need to look after the kids and get on with it.
I think the key is where you say you feel so let down. He IS letting you down in many ways. I'm assuming that despite that you want to stay married?
Ok - no penetrative sex till this is sorted and if that doesn't get him moving then go and see your GP and get referred for ligation. Simply ignore him. He'll have to look after the kids when you're not there. Go to your parents or friends to recuperate.