Am I being unrealistic?

So, my current boyfriend and I have been together for over a year now and we've liked each other for a total of 3 years. We are both going to be freshmen this upcoming schoo year. He treats me wonderfully, he is my best friend as well as my boyfriend, and we both have a great relationship with each other's families. 
My stepmother brought up that things will be complicated when we both go to college, which I'm fully aware of. He and I have discussed it and thought of ways to make it work. 
Is it unrealistic for me to think that it could last that long? I really love and adore him and throughout the years of us being together (as friends and a couple) we haven't had any big arguments. I'm 15 and he's 14 turning 15 soon. I'd just like to hear some thoughts from other people. Thank you!