I have been often misunderstood by others

When I see a couple holding hands, hugging, kissing, going out together, being there for each other and showing their love for each other through their actions, I turn my head away and start looking elsewhere. People often assume that I dislike the couple. But that's just not true at all.
I feel happy, and I wish them the best but I just don't like keep looking at them because I feel awful for myself. I feel sad. I ask the question to myself that why no one wants to be in a lovely relationship with me? Am I a bad person and can never be loved?
I have been told that I am an amazing friend. I guess, I'm a kind of a guy who can be a great friend but can never be loved.
It hurts. It makes me feel so stupid and sad. Probably it's Karma or result of bad deeds from my past life.