Falling Inlove

people who're in a relationship or just in love with someone, how do you know that its love and what does it feel like to be in love?
how do you know you like that person??

So, I have been in love with some one for years together now..... they don't know about my love for them and we still continue to be friends and relatives till date. By now I'm pretty sure that they will not see me as anything more than a friend and I wish to remain by their side "just" as a friend. So can u guys help me on how I should forget about them and if u have any experience pls share it with me! Because no one in the world knows about my love for them and this is the very first social platform where I wrote my unrequited love story.
And if u ask me why I'm not confessing.....its because they already have someone special in their life(although they are not married yet)......and there is nothing I wish for more than them to be happy together forever....