How do you know when your IN love?

Everyone has their own definition of love. My first boyfriend is the one I am still with to this day and I'm not afraid to say that I am in love with him. He's the only guy that comes to my mind when I hear the word love, couple, boyfriend... He's the only guy that I have sacraficed so many things for and because I WANTED to. We had our ups and downs and I admit I have had faults that really hurt our relationship. I think time apart reveals true love. And love comes when you least expect it.