Maybe very often, but not completely 100 %.
I know a pair which was divorced for several years, both had no other partners, and they came together again. Now you could say: the partnership was in no moment really at its end, and therefore it's no new love but the "old" one. Maybe, maybe...
In the end (not of time but of my thoughts) there is no reason to find an answer or to come to a conclusion if true love is possible only once: this does not matter for nobody, I think. It's only a somewhat romantic formula.