First, it’s great that you could be supportive of your son even though his coming out was hard for you. I don’t believe that sexual orentation comes from education or going to college, though the supportive environment he’s in now might make it easier for him to accept himself. But all of that has already been said. Here’s what I want to add:

I have two uncles. One of them gay, the other heterosexual. Now, my gay uncle met his husband 30 years ago and they got maried twenty years ago, and they had 3 children. He is still with his husband and he truly is an amazing father and a light to the world. My heterosexual uncle had one girlfriend in his twenties, and he never got another one after that. He is still single, child free and clearly has no intent in meeting a new match. So, if your main concern with your son’s orientation is the children he could have, please realise that it won’t matter that much. Sure if he wants them and he’s with a man at that moment, it’ll be harder for him, but not impossible.

Bisexuality has existed forever and there’s absolutly nothing wrong with that. Many amazing, happy, joyful, productive people are bisexual, gay, lesbian, trans, etc. You’ll be fine 🙂