Advice, please!

Bryana • Hey ya`ll, I`m a mother of two beautiful girls. I am a full time student and stay at home mom. I have an amazing SO that is a Afghanistan Vet. I`m very busy but wouldn`t change it for the world.
Ok I have two little girls that are almost 6 and 4. The man I am with now is not their dad. Their dad is still a very big part of their lives. They see him every chance they get. My thing is the man I am with now wants a baby. It's not that I don't want another baby, I'm just afraid of the age gap and my girls wondering why they have a sibling that isn't with their daddy. I'm just so torn! I don't want to make any wrong decisions. I need advice! Please!