I think this is probably quite a natural reaction when a child reaches a certain age or a pregnancy or birth of another child occurs.
I never though I would BF this long and I want to carry on up to the point it still feels right, but human social preconceptions about BF seem to swing from one extreme to the other, children should be weaned at "X months", FF, whatever or children should be allowed to self-wean.
Take a look at all sorts of other mammals, they don't go for "baby-led weaning", the mother gets up and walks off, earlier into the feed as time progresses, and she has no social preconceptions of what she is doing. Maybe her reaction is led by hormones.
Maybe you do feel less comfortable feeding your older child now (thank you for sharing as it is preparing me for what is to come), but you shouldn't feel bad about it. There must be other influences at work within your bodies making you feel that way.
Of course how you manage it is up to all of you as individuals, I just wanted to share a thought that might make you feel better for the way you feel right now.