Belief in God is rational.
Everything has a cause. So unless there is a first cause, then you would have an infinite regress. And then nothing could exist. Therefore there must be a first cause. Therefore God, the first cause, exists. QED. (You could prove the first step a priori that everything has a cause by noting that nothing can come from nothing. This makes it a priori, not just an empirical observation).
The temporary romance has to precede the permanent one.
I have have not even heard of situations where this was not the case.
That is how love works. You have an intense love early in life, but for some reason it does not last, and then you find the next one which does last. In Litvak yeshivas they say every shiduch [date] that does not work is one step towards the right one the "beshert." [The destined one.]
Going through this means one is one step towards finding the right one.
That is to say often people would go on endless shiduchim and never find the right one and the attitude was that each failed shiduch was one step toward the right one
The first one however must be real. It does not count if it is only immature love. Still there is something about it that makes it temporary.