I'll try not to ramble...

I'm in beginning the process of a divorce, without attorneys, as my (ex-) spouse and I are on amicable terms. We have a 4-year-old son. Although my husband is not biologically his father, he has lived as his father since before his birth. I do not intend to keep my son from him, regardless of the law. However, I want my husband to feel protected and confident that he will have access to our son.
He is on the birth certificate. But he is fully aware that genetically, he is not the father. Currently, we have been operating as if we have joint custody, and the arrangements have been smooth and argument free. HOWEVER, there have been two occasions that I've found my husband to take my son to a bad party and being intoxicated while he was in his care. We've talked about it and he understands that it's not acceptable and I still do not wish to keep my son from him. With that said, I absolutely do not want to put anything in writing committing to giving him joint custody or any kind of rights above the minimum, in case something like this happens again. I'd prefer to give him the minimum visitation and then allow him to see our son more often.
In Utah, if I include our son and custody arrangements in our divorce, the Office of Recovery Services will require he pay child support. I do not want child support. If I leave him out of the papers, I fear that he will be hurt and feel like he has no rights to our son.
What can I do here? Establish a parenting plan outside of our divorce, informally and "unofficially?" (not enforceable by the court) Does he have ANY rights whatsoever? Any way of having faith that he will be allowed to see his son, regardless of giving him my word?
We've been separated for almost a year and this is the only thing that's keeping me from filing the divorce. Help! Thanks

Were you married when the child was born or within a year thereafter? If you were and he is listed as the father on the birth certificate, then he is the LEGAL father and biology doesn't matter.

As far as I am aware, child support is part of the divorce settlement. I don't think there is a requirement to pay if the divorcing parties don't include it. I would suggest you check the law on that more carefully. However, even if it is required, you could set a minimum amount. Or you could just return the support to him. Better yet put it into a college fund for your son.

Were you married when the child was born or within a year thereafter? If you were and he is listed as the father on the birth certificate, then he is the LEGAL father and biology doesn't matter.

As far as I am aware, child support is part of the divorce settlement. I don't think there is a requirement to pay if the divorcing parties don't include it. I would suggest you check the law on that more carefully. However, even if it is required, you could set a minimum amount. Or you could just return the support to him. Better yet put it into a college fund for your son.

We were married over a year after our son was born.

Since he is on the birth certificate ( even if it was done as a fraud and could have legal issues about that latter) at this point he is the legal father and has the right to file for visitation though the court and pay child support.