Good question. the only answer i can come up with is to divorce or seperate, sometimes this is the best option.
Couples who stay together 'for the kids' will invariably pass along resentment and respect issues onto the children, and as children are a lot smarter and more perceptive than most adults give them credit for, the whole situation will be obvious.
The adults involved will either stay together up until the kids leaving home and then seperate, being forced to explain to the kids why they are now no longer together. Or they will stay together after the kids have left home, trapped in a loveless relationship with routine, habit and familiarity being the main contributing elements.
Either way, if the problems faced by the parents, force them to stay together for the kids, either some form of marriage guidance, to try to repair the relationship problems, or seperation would probably be better.
Divorce is never pleasant for the kids, but surely two independant parents, who are happy with their lives would be more beneficial to the children, than two parents locked together in a loveless arrangement.
With respect to your own position, you seem to be aware of the problems in your parents relationship, i would try to keep it in mind, and not allow it to influence your own relationships. Your parents stayed together for you and your siblings, even though i don't agree with it, i am convinced they did this with your best interests at heart.