What is this feeling?

I really liked this man last year It all started he liked me back aswell through obvious signs etc to cut a long story short I was really good friends with his work colleague they arnt good friends as the man I like was jealous I was talking to him but I and him were to shy to talk to each other anyway at Christmas me and his work friend hugged and we realized we liked each other I knew me and this man would never be together so I decided to give it a go with his work mate anyway everytime I see the man I get extremly strong feelings towards him but they are really emotional pains they go through me like lightning but they really hurt emotionally could someone please tell me why I feel like this it's so painfull x thank you x