Emotional Transitions

I'm having a hard time leaving the job I have now (and love) for this new job opportunity. And it's not because of the baby. Strangely enough, I feel more guilty about having a baby than I do about having a new job. yikes. either way, something's up emotionally/hormonally because even after my advisor told me he's positioning me to take over the grant in two years (as the co-head of the grant!), I started to cry when I got back to my office because I'd be away from this job for the next year (and they're hiring someone else to replace me). Rationally speaking, I think I cried because I'm replaceable, but I'm not sure. Also rationally speaking, I know this job transition is the best thing for my future and it will challenge me to try new things and gain new skills. Still, irrationally, I'm having a tough time with the idea of it.