Good for you for thinking about this now, for being aware of it and trying to articulate it. No doubt your feelings will shift around plenty, thanks to hormones and also this huge change coming in your life. But it helps to be aware and honest about your feelings.
When my DD was born, everyone was so "helpful" taking care of her 2.5yo big brother so I would have alone time with the new baby that I felt left out of a lot of activities. He would come home from these activities and run right over to the baby and be so excited about her, and was never jealous at all. But I guess *I * was, and I guess I was missing some closeness I had with him that was somehow diluted by her arrival. Now, 2 years later, it feels a bit strange to say this because we are as close and connected as can be, but at the time and for DD's whole first year, I experienced a kind of loss that I couldn't identify.
Turns out that DS's weaning (which coincided mostly with DD's arrival) was also a factor. With all the excitement of the new baby, I never gave myself time to think about the big changes in our lives as they related to me and my firstborn. We lost our nursing relationship and our bedtime routine (DH took over his bedtime and even when I did occasionally put DS to sleep he didn't want to hear the songs I'd always sung to him because he associated them with nursing and he wasn't nursing anymore.)
I love him so much that I often get tears in my eyes looking at him asleep when I check on him before I go to bed at night. So I can't believe that I ever felt distant from him, but it happened in some small way and it's over -- but it did happen.
I honestly don't think he ever felt it, but I sure did. What's so wonderful now is to see how much my kids adore each other (and they adore us, too!) There is so much love in our lives, so much love.
So anyway, be true to yourself and honor whatever comes up. It will be an evolving process, with lots of emotions -- and certainly some will be contradictory. Just be gentle with yourself, and see if you can stay in touch with what is going on for you on all levels (sometimes it's not so obvious) as you make the adjustment to having a sweet new baby in your life.