Love???

Today in my room, I've been wondering what exactly is love? I've never been in love before, and I've never had someone in my life whom genuinely loved me. I'm with someone now, and I tell him I love him all the time. I've just been thinking is it really possible to love someone, if you've never been in love before. How do you know what it feels like? How can you determine the difference between love and lust? Is it wrong to say I love you, if you're not sure of the meaning? The other day he questioned whether or not I loved him. His words that night affected me in a way that I did not expect. I began to question myself, I felt as if I could cry. I never questioned whether or not he loved me, and for him to do it to me hurt. I've showed him things I've never showed anyone. I shared moments with him that I do not want to share with anyone else. How can he question my love for him? Maybe deep down inside he's questioning his love for me.