And Rarity was running out of time.
This was the only way out, the only way I knew I could save her
I did what I had to.
The blood spell nearly killed me I lost so much blood I passed out right after the ritual was complete.
When I woke up, I dragged myself to Ponyville hospital, bloody and delirious. They thought it was a suicide attempt, and I went along with it.
But it worked. Rarity recovered completely within days. They kept me longer, to make sure I was ok. Rarity stayed with me the whole time.
I know I made the right choice.