Look, I have been there and I get it. You are one busy bee. Maybe you are taking 18 hours of classes, interning, working, leading a student organization, or any combination of these options. You have significantly less time than your friends and sometimes they just don't get it.
You will be okay.
There's a lot of pressure on you to be perfect, including being the perfect friend on top of all of your commitments. We need to accept something once and for all. Interpersonal relationships can be hard to handle sometimes. We all experience it. Dealing appropriately with people and giving them as much attention as they deserve is especially difficult when it comes down to sacrificing time you were going to dedicate to school or work. The word of the day is balance.
Life kind of sucks sometimes. Timing will not always be on your side. Your friends, if they are really your friends, will stick around for you because at some point they've gone through the same thing and understand. I'm about to throw you a cliche. Are you ready? Deep breaths. If your friends do not stay by your side even when you're stressed out and busy, then they are not really your friends. Shocker, I know. This just turned into an after-school special.
Maybe your friends are perfect, always understand, and even try to alleviate some of the stress. Maybe you're just having a really hard time dealing with everyone's expectations of you within your commitments or maybe you feel yourself getting frustrated because people are directly getting in the way of you achieving your goals. You're still going to be okay, I promise. Stress is an unfortunate piece of the university puzzle. You may need to reevaluate how much of yourself you can give at this time. Involvement on campus is usually the first to go in this case. Don't drop everything. Just back off a little bit until you can effectively handle it with your academics. Never sacrifice your academics! That's kind of why you're here, right? Mental health days do not count. Take a mental health day every now and then to keep yourself from going crazy.
The unspoken rule is that you get as many possible mental health days as you get free absences in a class. Don't waste them for petty reasons! You may regret it later. These act as a mental reset button and is one of the most valuable resources in your stressed out arsenal.
Finally, you are not lesser for being busier than other people. No one is going to resent or hate you. If someone would stop being your friend because you literally do not have as much free time as they do then you probably don't want to be their friend anyway. They're a jerk. You're pretty cool.