Complexity

I have a friend that asks me:
“Missing someone, loving someone should be a happy thing, but now why is it difficult for me?”

I answer him saying:
“It is difficult because she is not here with you but she has taken over your heart.”

Why should a simple thing be so complicated when it involve emotions and relations? Couldn’t it be as simple as “yes” or “no”? or maybe complexity is the beauty of it?