Although my marital stress is not too bad, I have to admit I have the same thoughts sometimes. Everyone I know at work who's been married and has grown kids give the same advice: these years are some of the toughest there are (i.e., when kids are small, mine are 27 mos and 6 mos). If you can make it through these years you can make it through anything.
Other experiences I have heard is that everyone I know who ended up divorcing all said after the fact, if I could go back, I wouldn't have chosen divorce, it is just too painful. Especially with children.
I personally am a child of divorce, and I survived. However, my father, who would have NEVER apologized for anything he or my mother did when they were divorcing, one day told, sheepishly, 25 years after the divorce, that studies show that even in families where the couple is unhappy, it still does less damage to the child than a child that has to grow up with divorced parents, no matter how peaceful and harmonious the custody settlement.
AND, every time I think about the real practicalities of being separate, EVERYTHING is more difficult, more expensive, more complicated: maintain two homes, two sets of clothes for the kids, two of everything, at home it will ALWAYS be just me to do everything unless ex-hubby has custody. For what? So I can start dating someone else? Because that is seriously the only reason why I would need to be alone. If I don't like him anymore, and there is no more passion, and if on our rare free time, we don't choose to do things together, so? It is still easier, and better for the kids to stay together.
Of course, this is all advice for a marriage with simple marital trouble (falling out of love, bickering, etc.). If you are undergoing any kind of psychological, physical or sexual abuse, then I wouldn't say any of this (but I feel from your email that you aren't).
And one more thing everyone keeps telling me: invest in your marrige. Yes, unfortunately, so much of this burden falls on the woman. Yes, many (if not most) women the world over carry the heavier load. That is just life. So if it means doing things you may not feel naturally inclined to do right now (ex. be generous to a non-generous man, be gentle to a non-gentle man, and so forth), you may just have to, well if you want to keep trying to make your marriage work.
Don't aim for the early-day passion, aim for friendship, when the children grow, apparently many couples go through a honeymoon period. Have faith?
This is all stuff I tell myself everytime I think the way you are thinking. It has definitely served me well, and when I make the first step, things set into motion.
"The solution to violence is peace, the solution to hate, love, the solution to greed, generosity." Your solution may be to show your hubby that you DO like spending time with him, make him THINK that he is not second to your daughter...