Good lord, 2-6 hours a day, that's how much of my 8hr work day's spent sleeping/eating/browsing.
If I may offer an opinion.
a) I get obsessive over things easily (still getting over my head-fi.org $1000 headphone fiasco)
b) I recently got into biking (wooo)
My girlfriend's got a 24" mtb and I have a 26" with slicks on it. It's hard for her to keep up and she's at the point where she's a) tired of being left behind and b) outriding her 24" now so very soon she's going to buy a 700c touring bike.
I realized that she wasn't happy being left behind all the time so now I try to a) keep her in my mirror and slow down so she's close enough to draft or b) let her lead.
Try getting him to ride earlier and starting dinner a little later, that way when he gets home from a ride, you two can still sit down to dinner and spend some time together.
Every saturday and/or sunday, we go for a nice ride around in the morning and drop by a cafe for coffee and a slice of cake. Show him that yes there's obsessive compulsive biking but then there's biking for the sake of spending a little free time as a hobby.
Take up the hobby with him and you take his road bike and get him a dual suspension mtb with big fat knobbies. I'm pretty sure you'll leave him in your dust. My girlfriend lost weight, shaped up, she looks better than ever. After all the compliments her friends and family gave her, she became a lot more willing to buy a new bike and grow with the "hobby".
Aside from getting counseling, you might want to show him that yes you're willing to take an interest in his hobby/lifestyle/whatnot but he's got to be willing to come to your level.
Find your own hobbies too or join a cycling club riding with people in your level. Meet some couples who manage their time correctly and invite your fiance to go riding with your group, get him to realize that there are avid bikers out there who are also able to devote time to friends and family outside of the sport.
Unless he's lance armstrong and brings home $$$ biking, you gotta do something about it.