Hi M.,
First of all, I just want to say that I will try to be as nice as possible when replying to your message. I've been on both ends of the spectrum here. My ex didn't want to be a "dad" either until my husband now showed up in our lives... so I get that.
I've also been on the other end of the spectrum with my husband and his ex with their daughter and how hard we fought to get the little visitation we have because she withheld and still withholds his daughter from us.
I'm not a psychiatrist or anything, but it seems if you do have an issue with him getting married so soon after the two of your split up (my husband's ex did the same thing and still has an issue with it 5 years later) and the lashing out at him is also what she does because of her jealousy... That's just how I see that.
Another thing is I don't know your visitation schedule. For instance, if he gets to see him every other weekend, once a month, etc... so it's hard to say.
Basically, what I am trying to say here is too many women "take" these children and hide them, brainwash them,etc. (I'm not saying you are), and it makes it difficult for men to have a relationship with their children.
My advice to you would be to give your ex a chance. I don't know the circumstances, but maybe there are reasons he can only come around twice a year. Perhaps you need to make it a little easier for him. I don't know the whole story, and I'm not picking sides here, I just hope that your son can have a GOOD, HEALTHY relationship with his dad. Put your feelings aside of what you think of him or his wife. Swallow your pride and give him a chance.
Good luck,
J.