When I was 23, I dated a 46 year old woman. My parents didn't approve, but assumed I was just doing crazy college experiments in my love life.
It will probably be very different in your situation since you will be married and in the "serious" part of your life. I am not sure how your family is, but I am guessing that there will be "concern." I think all you can do is to stress that you just want people to give this guy a chance. If they let down their guard, they may see that he is ok after all.
As for S's divorce, I think that if he was being all rational about it, then you must have fit somewhere in the equation. It could have been a small factor or it could have more like a catalyst which caused him to rethink his marriage.
As for support, I think that he just wants to know that you do not think badly of him for doing this. And you can be there if he needs to get some stuff off his chest. But I don't know him well enough to say this for sure. Maybe he is the type of person who likes to be challenged in his feelings? Or the type who likes to be explained how another person may be feeling?
Anyway, good luck and I hope it all goes well.