Im confused on how i feel

Having a baby is a fun, scary, and interesting thing. I am 4 months and 15 days pregnant with my second child. I am only 17. I turned 17 in September. My first child, Konor is 17 months old, he is so precious I love that child so much, even though i am not with the dad anymore, i havent been since about a week after he was born, i still have a man in his life, my fiance and i are so excited about our bundle of joy on the way. This is something that i have wanted for so long and now that i have it i am so scared. I am afraid that when i have this child everything between Cory and i are going to change. I am scared that Cory is going to get scared and he is going to run. Nick, my ex, ran because he doesnt quite now how to be a father since he never had a father figure in his life and that is something that is very important for a young boy to have in his life. And i was afraid that my son wasnt going to have that in his life, but he does and i am so happy for that. What am i going to do? How do i keep myself from feeling this way and just moving on and being happy? Any advice, im a little scared!