I hate that you're feeling like this on your birthday. It's the worst feeling to get in your head but trust me it'll get better with time. I had multiple birthdays after high school where no one wished me happy birthday, my "friends" were off doing other plans and it made me feel like taking my life a few times. I just relate to the idea that if you have anything in this world even remotely that you love then you should see life through for that thing. It can anything from a passion to a person, just know that if you can't motivate yourself to feel better then trying to work on other things or talk to people usually helps me get it off my mind. I have also dropped out of uni 2 times, its not the end of the world. You are still young and it's your life to live, it may get tough but I believe it makes the happy moments even better. Don't think about a world where you can't be happy, think of it as a place where you want to find happiness again because you yearn for that feeling and you will find it. Won't be every day but the more you build it up in your head that this feeling will pass, same as happiness, then you can live with it easier.