I think your fiance is being mature.
I think it's good to spend some time together as just a couple when you first get married, so you can get to enjoy being husband and wife, just the two of you together. Once there is a baby in the picture, you aren't going to have as much couple time.
If you finish college before you have the baby, you will be able to earn more money to help support the baby.
If you are pregnant and have the baby while still in college, you will spend a lot of time being very tired and possibly not feeling well, and you won't be able to do as well in school.