Years elapsed isn't important. Responsibility for something because of the time and effort you expended to build it is just an illusion. In the end, the only thing that matters is if it's a good or healthy relationship. Is it abusive? Is it helpful? Does the connection stress you out? Letting go of something toxic is important, even if it's a huge part of your life. Even if it's had it's talons in you for a decade, or less, or more.
Escape if you can. Be it a bad friend, or an abusive lover, a toxic workplace, drugs even. It's tough, but it's worth it. It's harder to fight than to roll over and take it- but at the end of the journey, it's worth the trouble for the breath of fresh air and freedom.
I know I'd rather die than to go back and live how I used to live- it's been less than a year and I'm already so much better.