For some people being in love with someone can cause them to think and do strange things. Humans have five senses; sight; smell; audio (hearing); taste and touch. Subconsciously a person can smell a certain scent once and never think of it again, but all of a sudden that scent may drift through the air and they remember the incident related to that memory and in your case it is the person you love. Example: If the person you love wears a certain cologne and you happen to be out and pass by someone wearing the same scent then your subconscious remembers that scent and of course you think of the person you love.
