Under the circumstances and seeing as you both feel the same way, I don't think it would be such a drastic decision to call it quits and go your seperate ways..... it's not the end of the world, you're young and I'm sure you'll both meet other partners that are much more suitable.
Maybe and maybe not. I think this time a little less impulse and a lot of thought should go into your decision.
You each should define why you are not happy and see what you can do to change it.
I was unhappy for awhile because I felt I did more housework than my bf in addition to working longer hours, I talked to him and we worked out a chore schedule that we can both live with. He didn't realize it was stressing me out, because he knows I enjoy grocery shopping, cooking, and caring for the animals, so he didn't think those things counted as "chores" to me. That was an easy problem to fix.
All relationships are work. Are you both willing to work for your own happiness? Will you support each other's efforts?
Ok so you moved too fast, but it sounds like you didn't do too bad. You can talk to him about your feelings, you seem to respect and care for him, he respects you enough to not smoke around your daughter. You think he's a good dad. You must share some similar goals if you can imagine a business together. You even love him! What important quality is missing? If the only thing missing is time - maybe you ought to make some.
You could cut and run, but it's not like you can go back to just being a kid, you will have two kids of your own. You will have to work, I'm not saying you can't do it, you just really need to be sure you want to.
If you leave because you're unhappy, you don't want to find out that you're still unhappy once you're out.