Why is this guy getting the "She's trying to control you" speech instead of the NRE speech?
You say you were fine with the relationship with your fiance until this new partner came along. What changed the original relationship that you are no longer happy with it other than someone came along who you have more in common with? Now you're concerned about your individual growth? Was that not a concern when you proposed to your fiance?
Is it just me or does your writing sound a bit like this has little to do with education and more to do with the women?
You are talking about life long commitments to both of them when you sound unsure about what YOU want out of your life right now other than skateboarding and hot sex. I'm not judging that by the way, I'm just saying you don't sound ready to be talking about doing anything until the day you die. Maybe stop trying to decide what you're going to do for the rest of your life and quit talking about those kinds of commitments.
You describe the new partner who you've known a little over a month as having the same place in your heart as someone you proposed to spend the rest of your life with monogamously. Where would you be right now if your fiances other partner hadn't come back in to the picture?
It doesn't seem very strange (or controlling) to me that your fiance is not thrilled with your idea of going to school because you talk about it as if you aren't going for the education, you're going to follow this other girl who you just met. She's not making up this paranoid delusion that despite your engagement you're leaving her for some young woman you can share a video game console and a bong with. It sounds like that is exactly what you are considering.
The school plans you've described are the new partners pre-existing plans. Your fiancees business is her plan. Why aren't you looking for a YOU plan? You are certainly going to be in a relationship with yourself for the rest of your life.