How much time do you spend together? I ask because I think it can be dangerous to assume that someone else is the cause of depression, and if you separate you could end up lonelier than now, but with half of your current assets, which might mean that you have to move away from your friends.
If you spend a lot of time with your husband/partner, you could start to do a bit more on your own or with friends, and if you already have your own interests you could build on these and make a life of your own within your marriage/relationship.
This would give you more to talk about when you are together, and might rekindle what brought you together in the first place, and may lift you out of depression.
Have you spoken to your GP about being depressed? I know a lot of people resist the idea; but I know a few people who have been really helped by a short course of antidepressants, so that might be something to think about too.
If after that you still feel that you are with the wrong person then you can leave with a network to fall back on. Starting again at 65 (particularly if you have to move, or if you don't have a lot of friends) can be difficult, as you may not have work where you can mix with others, and no school gates where you can meet others.
My advice, FWIW, is not to rush into anything. I'm sure you have thought things through already, but do try to put things in place first?
