Doubt kills a relationship. It's a well-known and undisputed fact that if you want to end a relationship, all you have to do is stop trusting the other person. What's less recognized, however, is how trust is just a part of a bigger issue: certainty. There is no way that anyone can ever be completely certain about anything in the philosophical or the scientific sense. But once you allow doubt to pervade the way that you see the other person, once you doubt the other person's motivations for being with you, you kill your relationship.
Your ability to make things work depends enormously on your level of trust and by extension your certainty about the relationship itself. When trust is undermined by doubt, the ultimate breakdown of your relationship will follow shortly. To make any relationship work, you must first eliminate doubt. This is not to say that you should be naive, but remember that many relationships have been cut tragically short because one (or both) of the parties just couldn't get rid of that doubt. Doubt is the ultimate killer.
So, how do you get rid of doubt? As far as I know, “it” really is a leap of faith. Remember the movie, Kate & Leopold? There's a deleted scene where Otis, Leopold's valet, says, "Love is a leap." You just gotta have faith because there are no rules; you have go by instinct and you have to be brave.
For the scientifically minded and those who refuse to believe that there are some things in life that you just have to trust--that there are some facts that you simply can't prove with the use of hard evidence or data, here's a little question and answer for you: Q: How big is the Universe?
A: It is infinitely big.
Q: How do you know?
A: I know because all theories and available data point to that conclusion.
Q: Theories? Has anyone ever actually gone out there to the ends of the universe and actually measured its infinite boundaries in order to offer hard evidence which prove that claim?
A: By definition it would be impossible to "go to the ends of the universe" because something that is infinitely big has no boundaries.
AND FINALLY: So how can you, or anyone say with absolute certainty that the universe is infinitely big if it's impossible to measure? Science, like love, has its own articles of faith. There are some things in this life that you just have to put your faith in. One of those things is Love.