You should read your own post. You say you have never been happy with him. There is surely someone out there you can be happy with.

You also say that what stops you from leaving is how he will deal with it. Guess what, that's not your concern. You CANNOT CONTROL how he feels. You cannot control his reaction. If you keep waiting until your sure that he will be okay with it, then you will never leave, and never find the happiness that you surely deserve.

I have never been married, so take what I say with a grain of salt. BUT, I have been in serious long-term relationships and had to make this same decision. My fiancee only made me unhappy with his refusal to commit and prioritize our relationship. Other things ALWAYS came first. We broke up and got back together numerous times. Then we broke up but stayed close friends because we couldn't bear to not be in contact. Then I realized that continuing to allow him to be in my life when he had hurt me so much was only holding me back emotionally. So I told him we had to break off all contact. He was upset, but it was my decision for what was best for me, so I could move on. And I'm much happier not dealing with his ******** and making me feel less than important.

Marriage is never something to end lightly, but if you are truly as unhappy as you sound, maybe it's time to separate. And again, remember that you have no control over how he will react, and it's not about how he will react. That should not be what makes the decision for you. You should make the decision on what is best for you. That's my take, anyhow.

Good luck,
Seesaw