Been there man. I think the bitterness is the worst part. My first marriage was a mistake from day 1 and we both knew it. But we didnt know what else to do so we stayed together and made each other miserable. 5 years we did that, and finally had to call it quits. It was rough becuase my son was only 4 at the time and just the look on his face when I was leaving was enough to make me want to stay. Leaving him behind killed something in me that never came back. But I knew it was better for him to grow up with 2 parents who didnt live together than to grow up with 2 parents fighting all the time. She remarried, she's happy, he's a good kid. I was a screwup as a father anyway, I probably did him more of a favor than I realized.
Then came #2. Like you, it was everything I thought I wanted, everything everybody always says a relationship is supposed to be. She had issues, she had 2 kids from her previous marriage, my parents hated her with a passion (and thats saying something, let me tell you). Matter of fact, I cant recall too many people that liked her. I was hooked though. We were together for about 2 years, then we got married. 11 months later I was moving out. She wanted more kids, I didnt. She wanted more freedom (read here, she wanted to sleep with whoever she chose to). I can handle "something happened", I cant handle it when guys who are supposed to be friends are boinkin my wife. Went nuts, beat the crap out of two of them, almost ran over another one ............ bitterness. Not rage, just bitter. It was supposed to be my chance to fix things, to make my life right, to have a real relationship. Instead it was more pain. Bitterness. Oh it was deep too. Lots of alcohol in there. Pot. Fights. Bars. More fights. lol You get the picture.
After a couple of years and a couple more screwed up relationships, I finally figured it out. Why I was so messed up. I expected somebody else to fix my problems. I put all my hopes on having that relationship set me right with the world and make up for my mistakes in the first one. IT DONT WORK THAT WAY. You either have to come to terms with who and what you are, or you have to fix it on your own. You have to rely on yourself to be who you want to be, you cant define yourself by your relationship. I was feeling sorry for myself because somebody else let me down. Everyone has their own goals and dreams, you cant rely on them to make yours come true. Make yourself into the person you want to be, make no apologies for who you are or what you are, and when you find someone who accepts that and still enjoys hanging out with you and doing stuff with you, then you've found someone you can build something with.
Dont go into a relationship expecting change. You'll get it alright, but never in the ways you expect. If you go in expecting someone else to change to suit you, or them expecting you to change to suit them, its never going to work. When you can both go in as individuals, and come out the other side still the same individuals and still liking each other, you've got something.
Preaching mode off.

I really wish you good luck getting on with your life. Its difficult, but it will happen.