I recently split with my dh. He is mid-50s (quite a bit older than me) and our family unit was his life.
But I felt as you do, and he wasn't all that nice to me earlier in the marriage. He did try really hard to change but it was too late for me; I didn't love him any more.
It's been awful and I really, really feel for you. You sound quite tortured and it's a horrible place to be in.
I was on a thread about this that is no longer active. You might be able to find it though, I think it's called 'How do you know for sure that you should leave' or something similar. It was started by Apty.
There are so many women in this situation. We are conditioned to do all the emotional work of keeping a family together and it's very difficult to overcome this pressure.
I'm not sure how to look for that thread - bit crap at MN - or give you a link but you might find it helpful reading if you can find it.
So sorry for you being in this situation. I am still feeling very guilty about my dh, but it is dissipating a bit. But if you are unhappily married, one thing you don't take into account is how difficult life will be after you have separated. I was so desperate to get out, but now I miss my kids dreadfully when they are not here, and I miss the family unit too, even though it was dysfunctional. You may feel relieved if you split, but you will feel isolated and cast adrift at times as well.
There is no easy answer. But re the guilt, you have to tell yourself that it is not fair on your dh to live with him if you don't really love him because it is now what he deserves. I know in my rational mind that this is true of my situation too, but it's not always easy to believe it, especially because my husband didn't really care if I loved him or not, as long as I didn't leave. Which is not fair on me.
Eventually, having spent years trying to keep everyone else happy, I have chosen myself. But sometimes I feel I have made the right decision and sometimes not. I don't want to paint a bleak picture for you, but the grass isn't always greener, it has plenty of brown patches! That said, on the whole I am happier without my husband though.
However much you want to leave, the actual process of it is very painful, maybe more than you realise now. It's early days for me, and I hope you get some posts from women who are further down the line and have lost their regrets.
Good luck.x