Have some company
Another saying goes that no man is an island. You cannot and should not go absolutely alone. You need company but the right company. If you value your current friends but they are an impediment to your studies, do two things. First, explain your desire to succeed in class and entice them to do the same. Second, if they refuse, politely say that you will have to devote your time for your studies and then leave all the fun to the holidays and vacations. If they are really your friends, they should understand and respect your wish. Give them time. They may eventually re-think their behavior and join you. But remain friendly to them. Greet them pleasantly when you meet and spend some time, but not in the same manner as before. They will get the message and understand you. You may even inspire them to follow your example. What is important is that you do not make them feel completely rejected and you remain friendly.
It may not be long before they are won over to your ways or you shall have found the kind of friends you deserve who will share your views about studies and bolster them. Water will always seek its own level.