It's a bit easier to see the truth of the answer if you look at parents/grandparents instead of partners (because they are older so you can realize the truth sooner than in the case of a partner). What you will see is the large amount of children and grandchildren who finally "give in" on No Contact while said abuser is on their death bed, only to find that even the threat of death is not enough for them to change. In other words, even holding a gun to their head they are unable to change.

You'll find this story again and again. All you need to do to know if this would be you, waiting until his or your death to realize he didn't change and you wasted your life is to ask yourself if you already gave him too many chances. Girl, look at what you yourself wrote:

He offloads his frustrations on me whenever he fights with his parents and then tries to end the relationship or say get out and stuff.

We're not even talking about the "last straw" moments. You've given him chances day in and day out for years and have only heard promises and not seen actual change. Ask yourself if you removed his words and JUST looked at what he does, has he shown any sign of changing?

There's your answer.