No. Matter. What.
They want more that you can possibly give. You could open every vein in your body and it still wouldn't be enough.
To top it off, they tend to be emotional vampires. Sometimes I think it would be easier if they were actual vampires. A stake to the heart and a broom to clean up the mess and the problem would be solved. Unfortunately, real life doesn't allow for any great Buffy moves.
However, real life does allow for speaking your mind and standing up for yourself. If you're a confrontation avoider like I am, it's awful, but it can be done. And I'm pleased to say, I recently did it. Unfortunately, I'll be experiencing the fallout for some time to come, but I believe the end result will be worth it. Life is too short for toxic people.