@Annabel80,
All right, let's start off by forgetting the other dude. Let's not get into whether he reciprocates your feelings. Recognize that crushes can happen, even to people who are,
actually, happily married. That doesn't mean this isn't real -- it just means it's not necessarily super-special. Sorry.
Right now, let's just concentrate on the Annabel80-husband relationship.
I am reading a few main points here:
(1) a lack of interest on your part, possibly also his
(2) you want kids. It's unclear whether he does.
(3) your fear of being alone
(4) you like him as a good friend, and fear you'll screw that up
#1 - if he's also uninterested, there's little point in continuing with the marriage. Get out now and stop wasting his and your time.
#2 - if you want kids and he doesn't, get out now. That should be a dealbreaker for any marriage. It just ain't fair to either party, no matter what happens, and it's not fair to any kids who may come along.
#3 - you're 29. Did you have independent time before marrying? You may find you have far more inner resources than you ever imagined. BTW, people a lot younger, less educated and poorer than you live alone every single day. **** happens, people become widowed and the like, and end up alone. Or they do it by choice. Alone does not have to be a horror show.
#4 - yeah, you'll very likely screw that up. At the absolute minimum, things will change. Divorced people can be good friends but there is no get out of jail free card here. There will be some hurt feelings, at least for a while.
I think you need to communicate. Find out -- does he want kids? Does he want to continue? You can have that discussion (perhaps in a therapist's office) without it being a screaming fight where divorce is threatened.
Clear your head of the other guy, at least for a while, and see what can happen with your marriage. Perhaps it should continue. Perhaps it should end. But don't add unnecessary complications into it right now. Take care of your own house first.