Well... love does hurt. A lot. And I can't deny that... Love hurts because love is a very delicate thing. And, it can actually kill you sometimes. There are tendons in your hearts that are nicknamed "heart strings". These heart strings can sometimes break after a deep emotional trauma and that could result in blood not being pumped enough. This is called "Broken Heart Syndrome". This could literally result in death... That's one of the reasons why love hurts. Having your heart broken (literally) us very horrible. I have experienced how horrible it is and all of the horrors with love. This is one of the reasons that I do not have a special one yet...
Anyways, the only reason love hurts is, well, science I guess... Apart from that, it's just what being conscious is like...