I think you should definitely bring it up to your T. You've also seen his wife at their house, and she was noticeably pregnant, right? So T is likely expecting you to ask about it. (He really should have told you himself though.)

I don't think your feelings are bad. I think it's totally natural to feel jealous. (I mean, I've felt jealous of MC's kids.) And I'm sure your T would understand. It's definitely better to talk about it. Both your jealousy and fears of T changing and your being less important. And you could find out how long he's planning to be on leave, too. I think he'd definitely want you to talk about it.