A mathematician friend of mine, when chatting on-line, types the emoticon “<3" to indicate "love". This two-character sequence looks quite a bit like a heart lying on its side. In fact, many chat clients automatically convert this character sequence into a heart icon. At some point it occurred to me that there is a certain poetry to this particular representation. Not only does it visually suggest the shape of a heart, but its mathematical meaning is, precisely, "less than three" -- an interesting assertion when applied to love. The next time you type this emoticon, you might want to consider that on some level you are asserting that love is just for two.†
A corollary theorem, as my mathematician friend might put it, is that you should never get involved with somebody who is already dating someone else.
<3 † “Less than three” can also refer to “one”. I am sure you will agree, mathematically speaking, that falling in love with oneself is merely reducing to the trivial case.