I believe you should tell him exactly what you think you should tell him but don't over think it. You already received Gia's assertion that he would be fine with you telling him how you feel, so just go for it. There can never be too much love! And in this situation, especially...this new babe is going to be SO loved. Wonderful! <3. Yay for love!! I may be looking at it very simply, but to me, that is how it all boils down.
Love is my religion <3