You say you are off-and-on-again? I say this is looking shaky. Don't be a cling-on and keep your passion in check; give her some distance or she may bolt.

On the other hand, IF it is true that she is becoming disenchanted with you, I'm not sure it is in your best interest to artificially pump life back into a dead relationship since you aren't married. Some things are just not meant to be, and there is no point in trying to force it. It is probably a bit early to be able to say if you are in this category.