Hang in there bro! I've been in your shoes and IT WILL GET BETTER! I know it sounds easier said than done but here is some advice that a friend gave me. If there is no chance of saving your marriage you need to TRY (the easier said part) to take emotions out of the picture and treat your marriage like a business.
Get suicide out of your head. It won't teach anybody a "lesson" and it will devestate everyone that has ever cared about you. Do you have kids? If you do, statistically you will increase your kids' chance of committing suicide. And if you do have kids, I know you don't want that. (It's the "if Daddy did it, why shouldn't I mentality") I've had two friends committ suicide. The last one was about six years ago and my heart still aches when I think about him.
Go talk to somebody! Yeah, it's cool that you're venting here but brotha, you need help. There is nothing pussy about asking for it. In fact, it would show that your man enough to realize that you have a problem and you want to do something about it. I had a good therapist that helped me through my bad times when I was younger.
Hang in there! It's not going to be easy but you will be happy again. Remember, nothing really worth having comes easy. I hate saying this because when I first heard it I wanted to kick the shit out of my buddy but it's true. (If your'e a religious man) Know that God will never put you through anything that you cannot handle.
Take care and be strong!