Hi and lWelcome,
You're right that you have no way of knowing if the drinking (self-medicating the pain) will stop when the pain stops. And, unfortunately, you're not even sure the pain will stop. I started drinking to self-medicate anxiety/insomnia/depression and I created a worse mess. I not only still had the above issues to deal with, but now I was an alcoholic. I hope your boyfriend's pain diminishes and I hope he stops drinking, but I would be surprised if it was that easy.
Take some time to get to know yourself and to understand why you chose this relationship.