As much as it may sound awkward, some of these things do happen. I have see situations where people have actually fallen victims of such both men and women. It's quite unfortunate but inevitable. Yes it is very possible for someone to love somebody else and not be loved back. This happens when one person secretly admires somebody else for sometime without mentioning it, and before you know it they are already falling in love without knowing it. Slowly by slowly they start acting like its a mutual feeling, when the whole time it's one sided. At some point when the other partner gets into a relationship, it becomes an issue of rivalrism, and yet you had no idea that this person was in love with you. That's why i always say communication is key in everything we do, communicate your feelings towards the person you feel attracted to and wait and see if they reciprocate, if they don't go your way and find love somewhere don't wait to get embarassed.