This one seems very simple to me. No disrespect intended to anyone who arrives here looking for an answer to this question, but if you want to save your marriage and you hating your step children is the reason your marriage is in danger, then simply stop hating your stepchildren. It’s easier said than done no doubt. Even your own biological children can be difficult to get along with at times. When children are giving you a hard time and they’re not even yours it’s easier to not bother trying to get along with them; but if you want to save your marriage you don’t have much choice but to endure them the same way any parent has to endure a difficult child until it’s time for them to go. And you don’t necessarily have to try to get along with them. You just need to try not to get into fights with them, just like biological parents often have to; and when conflicts do arise you have to understand and accept your responsibility as the parent figure.
You can leave your spouse to get away from your stepchildren, but since you say you don’t want your marriage to fall apart because of your step children then try reminding yourself that there are many biological parents having as hard a time with their children and they can’t just pick up and leave. For you to pick up and leave would suggest your marriage was more a take it or leave it situation for you and when the going got tough you decided to leave it. In that case you haven’t really lost anything because if your marriage wasn’t worth enduring the hell that parenthood or step-parenthood can sometimes prove be, in order to keep the marriage, then the marriage wasn’t worth having to begin with.