Like infatuation, this obessive momentum you write of just doesn’t last; to find the long-term slow burn that will actually carry you through, you should think of and write down your long term and mid term goals (concrete, assessable stuff, not ‘I want to be fluent in 2 years’ type stuff) and your overall reason(s) for learning the language. This will be less exciting than the initial rush you felt, but will be far more enduring.
Still, you seem to be knuckling down with an impressive study schedule (something I’m kicking myself for not having done when I was there), so it sounds like you’re on the right track.
Motivation will ebb and flow - totally normal, and part and parcel of this long-term language-learning journey we’re all on!
No substantial successes yet; the joys are small but frequent - today’s was reading Leebo’s post about yojijukugo, and being able to appreciate some of the beauty of the idiomatic language.