(haven't read all the posts, just responding to OP on page 2)
I'll come out of lurkdom to add my 2 cents:) I am a carrier of severe hemophilia, and have 2 sons that have the condition. (we did not know I was a carrier before I had my older son, so this was not an issue when my husband and I were dating) It is certainly something to be aware of, and take into consideration, but it's very treatable. (though very expensive to treat--DHs job doesn't pay great but has great insurance, which for us is more important)
With older children they usually do preventative treatment (to get their clotting factor up to normal) 2 or 3 times a week (for us, it's a 15 minute thing in the morning, like brushing teeth, and my son finds it about that entertaining--needles are not a big deal to him at all--we hope in the next year or two to have him infusing himself!) and then they go about normal, daily activities. School, gym, camp, sports, etc. The only things they are told NOT to do was football, full-contact hockey, boxing and wrestling. Anything else is fair game, they lead totally normal lives. I know in the past hemophilia was a very life-altering thing, but treatments have come a long way and are getting better all the time.
For what it's worth, also, the chances of having a son with hemophilia are 1 in 4 for carrier moms. It's x-linked, so mom and dad don't both have to have it to pass along the condition.
I'm sure your DSs sweetie already has seen first-hand exactly what living with hemophilia entails, though, and certainly might have her own thoughts on the matter. Has he discussed this with her at all?