I think you should tell him how much pain you feel because of it. I don't know if I would use the words "I love you." You would know better than me if that would freak him out or not. You could call it attachment or missing being with him. Or that you think about him all the time and that you worry he doesn't like you when he doesn't respond to your texts.

I'll be honest, I think that maybe some of the solution to how painful this is would be for you to try to deepen some of your other relationships. And maybe your therapist can help with that...help you figure out who else in your life might be safe to share a little more with, etc.