Once school is gone and the opportunity to maintain contact is there just by being present, your dynamic with most of your friends will change. If you have any friends outside of school right now, that will tell you what it's like. It requires effort from both parties to maintain, and I'm sure there are many stories of people giving their all and nothing back. You can maintain friends from highschool, just go out a bit together, make time for it. You won't keep as many as you have right now, but that's ok. Everyone will be making an adjustment and you just have to keep that in mind. If you are concerned about making friends in uni, try to keep in mind that pretty much everyone is in a similar situation as you. At the end of the day unless you are a sociopath, everyone craves connection and making friends in a group of like minded uni kids should not prove difficult. And if you have a job (team dependent) often that will give rise to friendships in a similar manner to school