It's an interesting point you have there, and also a very pessimistic view of the subject. "Love" as it occurs in Western society isn't the same as "love" that occurs elsewhere, or love that occurs ideally, and a lot has to do with the cultures people are raised in. Almost every instance you cite as a reason one would be lying about being "in love" is a dysfunction that occurs as being part of a society that heavily values personal privacy and individuality, as well as having demi-taboos. There are plenty of things one cannot communicate with one's partner, even restricting oneself to ideas (which are very malleable) as opposed to actions (which one can never take back), without fear of unintentionally ending the relationship. Of course, this occurs everywhere, but some reasons for dissolution of "love" are more common to some areas than others, reflecting the values and norms of those culture areas. Ideally, one should be able to talk to their significant other about any idea they may have without having to worry that the subject matter is too inappropriate, or too ridiculous.
Outside of that, hormones have a lot to do with feelings of love, which explains why abusive and abused people so often stay with each other, despite whether or not they rationally understand how bad they are for one another.
