K.,
First I just want to say that, excepting the medication, I have been in your shoes. I know the depths of emotion your dealing with. I'm sorry that so many people face this situation everyday, but I'm also here to say that you have reason to hope for a better future.
Someone earlier said that you and your kids deserve to be "happy" to paraphrase, and that to be happy you probably need to split with your husband. Let me propose a different point of view: You and your kids DESERVE to find out how people who are having a hard time getting along, agreeing, people who made a promise to love each other through thick and thin, work things out and live a better life than they were living before.
It's true that when your kids grow up, they WILL remember this. They WILL remember the tension, the sadness, the fear they felt. Is their fear going to turn into a shattered reality? If you choose to stick it out, to change your relationship for the better, then you give your children a beautiful gift. They will remember how you handled this and will be able to work out the tough problems in their lives too. By committing to work on this relationship you show your kids how to keep a promise though the odds are stacked against you. You're showing them true love. They deserve that.
If you look into it, there is overwhelming evidence (all over the internet, books) that families, husbands and wives, who stick it out, are doing what's best for their kids. Giving up is not the best thing for your kids. And I would say, it's not the best for you either. I wanted to give up many times in my relationship, but I didn't and I would never trade who I am today for who I was at those times. It was worth the pain, the self-discovery, the change, the GIVING-IN to my husband with a smile and letting him lead the way...yes, even that.
I didn't lose happiness. I found myself, and my love. The passion in my marriage returned. It's possible. Don't give up, don't let go.