At 18 you are at a very vulnerable age...you are a young adult with the whole world at your fingertips...wow I would love to be that age again - knowing what I do now that is lol. Ok, first thing to do - stop doing the 'self pity' thing and start living! Sure you miss your mum that's understandable..but hey, she wouldn't want to think of you moping around being sad..she would like to think you were busy studying, meeting new friends and having fun! Don't hide yourself away - others are missing out on meeting a cool person ~ You !
Push yourself out there and join in some activities.. you will be amazed how good it feels being with like minded people..and will soon forget about all the negative stuff you are carrying around with you. Keep in close touch with your mum..it won't be long and you will be able to tell her about your new friends and all the activities you have been doing..she will be delighted to hear you are happy I am sure...because as parents all we want for our children is for them to be happy..
Take good care.