You'd be surprised as to how many people want to leave, feel that they are in this type of relationship but just don't know how to leave.
Of course things get complicated with children or marriage or living together however, I do believe for your own sake of your spirit and personal well-being, there should always be a way to leave a toxic environment, it is not easy but it is possible. It is all possible.
1) Become Aware
If this individual doesn't make you feel good, more often than none, listen to that. If someone shows you who they are, LISTEN to that. If they are verbally abusive, emotionally and god forbid physically, these are definite red flags. If you feel worthless, un-important, sad, depressed or to a lesser extreme, just overall stressed or irritated while in the presence of this person. Start analyzing why and how you feel how you fee.
2) Act on it
Decide what to do, make a plan. Start communicating to resolve the issue, if you're already passed that stage, allow yourself space to really look at the situation, create lists of possibilities whether it be a schedule, allowing you time, more communication or maybe counseling for you guys or writing out ways you think you can both improve. Meditate on it also, get a clear head. What ever you do, stop enduring a toxic aura. Make a move, an effort to do something, the result may be not to leave it but the toxicity will and should end.
3) Become selfish
I don't know why such a negative connotation is involved with being selfish but the truth of the matter is that you need to put yourself first in order to living healthy. Again, with kids in the picture it's always more complicated, and sacrificing a lot for them will always be a factor but remember how you want them to grow up, the values you want them to have, and would you wish any toxic energy upon them? Become selfish in your thinking, know what you deserve and should have or not have in your life.