I don't know how to say no to my bff and she ended up sort of bullying me?

She is taking you for granted and you are letting her. There have to be boundaries in your relationship so that you get the respect from her you deserve. At the moment you are letting her walk all over you and she probably despises you for it. You are the one with the laptop and she's the one who uses it...for 4 hours? Wow. For starters tell her your laptop has broken down and has gone off to the menders. See if she stays with you for that quality time then. I suspect she won't. That will indicate how much she actually does like you or if you are only useful to her for computer time. Then, after a week or so when it 'comes back' from the repair shop - just don't let her get on it any more. Blame your mum. Tell her your mum doesn't want any of your friends using it anymore or it will be taken away from you because your parents don't want it broken again. If I were you I'd tell your mum that this is what you plan because she'll be backup for you. I presume she doesn't know what goes on in your bedroom when your friend is with you. She probably thinks you are having fun and will be horrified to know that you read while your friend uses HER electricity etc to chat on FB without her parents knowing. I don't think this girl is a real friend - let alone a best friend. I'd phase her out gradually if I were you by just being unresponsive. When she wants something - oh sorry, you don't have it handy for her. You are not being selfish. She is. Don't have an argument with her, just gently phase her out of your life (she'll find someone else with a computer soon if yours isn't available) and find yourself some proper friends.