"Therapy" in English is a broad term, basically meaning "treatment". You could have physical therapy ("physiotherapy") to help recover from a broken leg, for example. For mental health, one kind of therapy/treatment is "psychotherapy" (where you talk about your feelings to a professional). Sometimes people casually refer to that as simply "therapy", but in a general context that is not the definition. Therapie in German has the broad meaning.
"Will", like many of the modal verbs, doesn't have an ending for the "ich" and "er, sie, es" forms, as they historically originate from past tenses.
(Similarly in English: we say "he will/must/shall come" and not "he wills/musts/shalls come".)
So it's ich/er will, ich/er kann, ich/er muss, etc.