Maybe it stems from you're parents and childhood. Growing up in a home where parents hated each other, nobody said I love you could suppress love feelings. I can relate. I grew up in a home where I love you was never said, parents had a rocky relationship. Plus there was abuse. I have difficulty saying I love you too. I'm not in a relationship.

I would discuss with you're bf what you're experiencing. It will help him understand why you are feeling this way.