I have always said it first. Only one time it wasn't returned immediately and we were both young and he did eventually say it just not right then. With my husband I said it only two weeks after we really started being with each other. We had known each other a month prior to being together intimately. When our relationship turned intimate we never spent a night apart again until after we were married. I just knew with him. I knew he loved me too. I knew we would marry I just knew. We met in November, I told him I loved him in December he said it back lol. We were engaged in March, and married in July. Sunday we celebrated 8 years together. Sometimes you do just know.
Don't fret over saying it, it isn't worth it. Do what comes natural to you chances are he feels the very same way you do.