Hi!
As guinea pigs are social creatures, it is quite likely that Winston is lonely without you around and without a friend to keep him company. Socialization is critical to guinea pigs, a depressed and lonely piggy can even start to refuse food in the worst case. A single guinea pig is really not ideal and especially not an ideal pet for a busy person, whether that be a person who works a lot or a busy student.
The absolute best thing you could do would be to find him a friend. I am sympathetic to money and time struggles, but I do find that generally two guinea pigs do not cost much more money or time than one. I am not sure this would be the best option for you however if you say that you already struggle to care for Winston alone.
Another option would be to find someone else to care for him who can provide him with more attention and a friend to live with. If you would really not at all be able to provide the time and care for a second guinea pig, this would be the best option. I know this is not the easiest thing to do, but it certainly sounds like you care about Winston and that would be the most humane and kind thing you could do for him. It is a very difficult situation to be in as a pet owner, but I think we have a responsibility to realize when we cannot give our pet the quality of life they deserve.
There are many great rescues out there who could help you on your journey to either finding Winston a friend or finding someone else to care for him. Do you live with family that could keep him company while you are busy in the meantime? Maybe you could explain that interacting with Winston is critical to his health and happiness. It does sound like Winston is struggling in his current situation, it is nice that you are trying to find out what you can do to help him.