What is the evolutionary significance of the sensual component of Love?

Well, to answer your question, one has to ume that the spiritual substrate would in some way ist in evolution. I've scratched my head, but the only thing I can come up with is that the sensuality accompanying and attraction increases the likelihood that a man and woman will stay as a couple, which increases the likelihood that their children would reach breeding age. I'm not sure this is the kind of answer you are looking for, though. But I can come up with no way for sensuality to cause evolution of the spirit which would ist in the continuation of the species, since the species continues whether the breeding couple engages in sensuality or not.