Alright, mahna_mahna dragged me here to this thread. I've lurked for a couple of years, just never registered until now.
First of all, regardless of what anyone tells you, it is NOT your obligation to make sure your son hasa relationship with his father. It is HIS obligation as a father to get off his ass and decide what kind of father he wants to be. If he wants to be there, HE needs to take the time to make the arrangements and see him. He needs to be respectful of your and your time and not expect you to drop everything for him. Regardless of it being "his son, too," YOU are his mother and primary caregiver. Your schedual is the one he needs to arange around, not you his.
I don't mean to sound like a bitch, I've been in very similar shoes to where you are. Next month will be two years since my son's sperm doner has seen him. I haven't heard anything from him since I took him to court for child support and for custody when my son was a year and a half old. Up until then, I bent over backwards for him to try to keep him in my son's life. He went to stay with him every weekend. I never told him no when he wanted to come over or wanted him for longer than two and a half days. But you know what I came to find out? My son wasn't even with him on the weekends. As soon as my son was picked up, he'd be shipped off with his fathers roommate/exgirlfriend and her fiancee. My son was always with her. Most of the time, she woudl be the one that picked him up or dropped him off at my house because his father was at work or sick or playing paintball. Yes, playing paintball was more imporant than bringing his son home.
The last time my son went with him for the weekend, his father had to pick him up because I had a major fallout with his roommate when she tried to tell me how to be a parent and she was never allowed at my house again. Do you know what my son did when his father took him from me? He screamed. He screamed and cried his eyes out and fought to get back to me or to my mom. That was when I knew for sure he never spent any time with him. That was the hardest thing I've ever done in my life, letting my son go with him. And that was when I decided enough was enough. I sat down with an attorny, filed for child support and custody and haven't heard from him since. He never responded to any of teh court documents and didn't show up for court so he was defaulted against. He has visitation, it says so right in the paperwork, but he never tries to see him. No phone calls, no emails, nothing. And I will be damned if I chase him down again. If he even bothered to answer my calls or emails and came to see him, he wouldn't want to be there. And children can feel that. My son would know, just as he always did, that his father didn't love him or care about him. The times I DID see them together, my son had nothing to do with him. He didn't like it when he picked him up or tried to play with him or anything. It was really sad.
The best thing that you can do is file for child support. Either with an attorny or DHS is up to you, but it is something you need to do. This will make him decide what kind of father he wants to be. Regardless of whether or not he has a job, they will add up how much he owes you and will start adding onto it. If he still opts to not seek employment, they can throw him in jail for willful unemployment. That, if nothing else, can give the incentive to shape people up.
There is nothing wrong with wanting help from him financially. That doesn't make this about the money or "put a price tag on the relationship," as someone put it. What CS is about is ensuring that he is at least being somewhat responsible for their child. My ex only pays CS because it was court ordered and garnished from his check every pay period. I know the only time he ever thinks about my son is when he sees the deductions on his check for the child support.
Trust me, this is something you need to do for your son more than yourself. Don't wait as long as I did. I put my son through a lot of unnessecery shit in hopes that by bending over backwards for his father and letting him walk all over me he would be in his life. It didn't work. It will never work. If he isn't in your sons life because you don't call them, then that's on him. And your son WILL understand this. As long as you are not keeping him from him, your son will see what kind of a father he is. And he is not going to blame you for not trying. Your son will blame HIM for not trying.