Feeling sad on the inside

As I write this journal entry...I am having a hard time explaining how I feel. I went to bed earlier with my boyfriend and we said our goodnights and I said "I love you" and he said "I love you too" but somehow it seemed as though it were just an automatic response and that he doesn't really mean it. I know I might be blowing this all out of proportion...but this is how I really feel, and it makes me very sad.
There are so many thoughts going through my head, like is he thinking of someone else as he drifts off to sleep? He is the only one who could answer that...but I don't know how in the world I would bring it up to him.
I feel like bawling my eyes out right now...that is how sad I am feeling. I wish the feeling would just go away...but everytime I try to close my eyes and go to sleep, my mind wanders.