You have 7 days to remove or 'deal' with the tadpole before you die, I imagine that there are multiple solutions to the problem that depends on what you are willing and unwilling to do. To paraphrase a certain pirate.
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Raphael offers one very straightforward deal. In exchange for your soul, he will cure you of it, allegedly. The thing with Devils is while they can't lie, they can bend the truth. Selling one's Soul is not done lightly in the Forgotten Realms. Denied your proper afterlife no matter which god you worship or your alignment, and condemned to a miserable existence as cannon fodder for the never-ending Blood War between Demons and Devils.
Constantly using the Tadpole/Worm allows it to get more easily invested in your delicious brain, remember the wording whenever we saw Swen us the worm "sated". As in the beast is slowly eating more and more of you the more you use it. Nothing major at first it is a little thing after all. But the more you use it and the longer it stays in your head, the more and more it will take.
However, you deal with it is on you. Sell your soul to a Devil? Look for a Githyanki creche? Look for a powerful cleric to heal you? Find a Wish spell? Tick-tock, tick-tock.

Evil always finds a way.