The worst thing in the world is saying "I love you" and then waiting for the response. You don't want it to be forced, and you certainly don't want it to be absent!
Saying those three little words is kind of like taking the next step in the relationship. It sounds like you're really ready and maybe your boyfriend isn't.
Women are often afraid that their partners think they analyze the relationship too much.
Men are often really afraid of allowing themselves to feel vulnerable and open.
He Might Resent It
When the woman comes from an insecure place and says something like, "well how are you really feeling right now?" he knows what's expected of him, and he might resent it.
Don't Push It
I guess my suggestion is don't push it. If things are going well, then wait for the mutual feelings and expression of real love to blossom. If you feel like you need to analyze the relationship, do it from a distance, with family or friends.
On the other hand, if the time feels right and YOU are the one who is a bit scared, then do it right. Take him to your favorite place, shower him with affection, and tell him.
I Have Said it 6 Times
I've broached the subject of those three little words a total of six times. With each person it was different, but I have never regretted telling that person I loved her. The truth is that I still do love each of them. The feelings of love, once let into my heart, never really go away. It's like a river has been released from behind a dam and nothing will ever stop it. Distance and time might turn it to a trickling creek, but the love is still there, flowing, continuing.
So, I guess you'll know, and it will feel different, and a bit strange, but when it's there, it's wonderful.