Should I give in and have a baby with my fiance

I am engaged to a great guy...he's everything I've ever wanted in a man. Problem is, he desperately wants a baby together. I have 2 chidren from my previous marriage and he has 1. We will all be living together next year...so doing the blended family thing. I don't know that I want another baby as my youngest is about to start school and I can finally go back to work and have enrolled to study (a dream I've had for years). Am I being selfish? I love my kids, but just don't know if I can go back to all that baby stuff again!!