Verb for "... his passion"
Fulfill might work:
verb (fulfills, fulfilling, fulfilled)
1.0 Achieve or realize (something desired, promised, or predicted):
he wouldn’t be able to fulfill his ambition to visit Naples1.1 (fulfil oneself) Gain happiness or satisfaction by achieving one’s potential:
ODO Emphasis mine
Perhaps indulge
Allow oneself to enjoy the pleasure of
Oxford Dictionaries Online
... where I could behold his passion at work ...
Is this the girl talking, or what? I thought it sounded Romance, thus my suggestion :-)
Blackwood's Edinburgh Magazine - Volume 36 - Page 105 1834 - Full view
I flew rather than ran along the bank, till I arrired opposite the spot where I could behold him faintly struggling to disencumber himself of the cloak, which impeded all his efforts, and would have reduced him, in a very few minutes more, to a ...
One may also "realize" a passion. This is the verb I would use in the case of a fascination becoming practice and employment.
...where I could sate his passion.
verb
1 Satisfy (a desire or an appetite) to the full:
sate your appetite at the resort’s restaurant