Well.... I see that you are WILLING to support him, but your being ABLE hinges on what exactly he's asking from you to provide for him at this time, doesn't it?
What kind of support does he want at this time? Later down?
- To just be able to talk to you about his poly stuff -- feelings, ideas, crushes?
- To be able to date? Take on a lover? Now? In the near future or distant future?
- Something else?
The conversations you have to sort it out will differ depending on what it is he wants. For instance...
- For listening about crushes, you have to be willing but don't have to have conversation about birth control/STD prevention.
- For taking on a lover, you have to be willing and you do have to have conversation about birth control/STD prevention.
That's just a super simple take on it -- there's lots of other things you could talk about.
But likely it will be a series of talks. Those conversations could also cover what YOU might need at this time? Or later down?
Here are some links. I'm sure other people could offer more.
You both could spend time talking out what you expect from yourselves and each other. What changes and what stays the same in light of his self-discovery and what it is he is requesting from you in terms of being supportive toward him.
From intangible things like your beliefs about love and loving to very nitty gritty practical things like... "where in the family budget are your dating expenses going to come out of?"