Does love take time to grow?

I am currently in the midst of making a huge decision. My boyfriend says he isn't in love with me but is " falling in love" with me and is the happiest he has ever been with a girl in his life. We have been together 9 months - and he admitted he had fallen in love with his two previous fiancees more quickly than this. I know he has been burned in the past so is being more cautious - but I am worried he should know how he feels by now and if he doesn't he will never love me. Am I being over dramatic or should I walk away to risk further heartache in the future?