Dear Martin:
What you wrote above makes sense to me. And, thinking about it, one cannot argue with a … spark as a reasoning, just you wrote, a spark igniting and then disappearing cannot be explained. A spark is really not a solid basis to a relationship, because it is unpredictable, because it cannot be explained (and even if explained, an explanation is not necessarily going to re-ignite it).
A spark is here today, gone the next. Better be with a partner whose reasoning for being and staying in a relationship is not that elusive spark.
anita