The same thing you would do if you had a straight son.
Having a gay son is always made a spectacle
As if preparing for your child’s potential queerness is on par with being diagnosed with some terminal illness.
It’s not a tragedy to have a gay son. Not an inconvenience. Not some hypothetical hard premise to make small talk about at a dinner table. People are gay. People are straight. And all sorts of in-betweens.
What would I do if I had a gay son? The same thing I would do if I had a straight son.
But that’s not an interesting enough answer for you is it? Watch the satirical comedy sketch on what to do.
And enjoy the reaction people give you when you use this answer to such a silly question.