I consider myself a martyr for staying in this relationship.
Don't. Absolutely don't. Staying isn't helping anyone. It's not helping you, it's not helping them. Listen, I have been in abusive relationships from both sides, I have been abused and I have abused. Someone who lets you abuse them is not helping you. It doesn't make you happy. It makes you feel miserable and you lose respect for yourself and for them a bit more every time, and yet you don't know of another way to deal with one another, and when you stop they are so used to being abused that they act to provoke it again because it reassures them.
And at some point you feel like it's what you're expected to do, whether it's true or complete crap. And someone staying does not make it less so. Someone staying makes it feel like they're staying because they want things to be that way, and if you stop being abusive, they might leave you.
You need to stand up for yourself and leave. And if a relationship ever shows the signs of going that way, stand up for yourself right away, stop the vicious circle before it starts, establish a clear line.
But now it's too late for that. The only thing that can help them at that point is losing you. And maybe next time they won't start the cycle again, or they'll find someone who won't take any crap from them. But right now, the best way to help yourself, and the best way to help them, is to go the hell away.
It's not just liberating for the person who is abused to get away from the relationship. It's liberating for the abuser, too. There is something wonderful about not being an abuser anymore. There is something wonderful about dealing with people who stand up for themselves, people you can consider your equals.
I don't know how many abusers are at a stage when they can take a look at themselves and stop, but what I know is that it's hard to do while in a relationship, and I assume it would be much easier while not in one, so on top of saving yourself (which you really need to, and then work and rebuilding yourself, your self confidence, your self respect, and know that you are good and worthy and can do it all), you might be saving them, too.
Yes, they need help. But the only way you can personally help them at this point is by not being there for them to abuse.
Good luck. It's hard and requires you to be brave, but you can do it. You are not a martyr, because martyrs sacrifice themselves for a cause. There is no cause, so you are just sacrificing yourself. For nothing. You're committing suicide by staying. Get away.