Is this man in danger, and what is the ruling, and in what does his cure lie, if he commits a sin relying on repentance, and he says, "I will repent, God willing," and even says, "I will associate partners with God and then repent"?

Whoever sins with the intention of repenting later is in danger. Resolving to commit disbelief in the future is immediate disbelief, unless one is afflicted by intrusive thoughts (waswasa). Claiming, "I will repent, God willing," is not a commendable hope but a bad wish, and Allah has warned those who indulge in wishful thinking. Allah the Almighty says: (But you yourselves tempted yourselves, and awaited, and doubted, and were deluded by aspirations until the command of Allah came, and the deluder deluded you concerning Allah.) He also warned against being deluded by the worldly life, as it leads to negligence. Allah the Almighty says: (And the evil consequences of what they did will become apparent to them, and they will be engulfed by what they used to ridicule. And it will be said, 'Today We will forget you just as you forgot the meeting of this Day of yours, and your refuge is the Fire, and there will be no helpers for you.' That is because you took the verses of Allah in ridicule, and the worldly life deluded you.)