Lady.....At first reaction, I thought I had the answer to this, instantly.......but it's really a question that I believe requires some deep thought and complete honesty.
The process of "falling in love" (IF I even remember correctly) by it's very nature, is mostly guided by the heart and directed by emotion, passion and the senses.....It's not really one of those events in life we approach with logic, text books and formal inquiries. Add to this that both parties are on their best behavior, putting their best foot forward and choosing to IMPRESS one another.
The subject of "trust" may not even present itself at first.....and IF it did, would a person "in love" even allow themselves to recognize it? Point in case: I can never forget when a good friend of mine confided to me that the very things about her husband she thought were so sweet & adorable in his behavior, through the years, became the same things she grew to hate about him. Scratch your head on that one, but it happens more often than we may care to admit.
If the "trust" you refer to is the undying trust of fidelity......We can believe it, want it, and feel confident about it....BUT.....how many of the 50% divorce rate are due to cheating? MOST of them.
If we insist upon a 100% fool-proof FOREVER unbreakable trust in another human being, it seems to me, no one would FALL IN LOVE, ever. That's a pretty sad thing to think about. The truth usually is.