Sounds like you have been married for more than 20 years, not just living that long.
Seriously dude, you should get out of the relationship. This situation can't be fixed. It would be a terrible shame if you got married, had some children and then split. You have many, many years ahead of you before you should even worry about settling in to a permanent relationship. Sure, relationships when you are young can work out for life, but most don't.
As mentioned by others, you seem to already know what you want to, and need to, do.