I don't think your feelings are bad or wrong at all. I am sometimes jealous of my T's kids, and they are not even babies anymore. But I would love to have had even one parent like my T when I was a kid. (Or even to just have a parent like her now!) I don't think she is a perfect parent, but I do think she listens to them and cares about them and wants to encourage their healthy development. How could anybody not want that for themselves, especially if they never got it when they should have?

I do think you should talk to your T about your feelings. You found out in a pretty innocuous way, and it sounds like you already had some hints that she was pregnant anyway. I would feel burdened by getting all that information about the baby, especially if I heard it all at once when I wasn't expecting it and from somebody besides my T. Talk about your concerns about things changing, ask about paternity leave, tell him all the stuff that's coming up for you. Your access to your T might not change as much as you think it will, and regardless I think you will be more settled if you know what is coming.

I don't know if this is relevant or if you're interested, but I ran across a book once called something like Awaiting the Therapist's Baby that had some interesting thoughts about how clients respond to therapists expecting babies. It was more about pregnant women, but I think the same feelings would be relevant to dads. It was one of those Google Books preview things.