welcome to pc, lala! glad u found us. there have been some really good replies to your question. knowing your parents love you and want you to be ok is a good start. they will understand when you tell them. they will want you to get help. i'ts not like you caused this. thank goodness you are willing to get help. that's a huge step towards getting better. i like the suggestion of writing the letter to your parents. it may make it easier to start the conversation with them.
i know it may hurt that your friend is setting boundaries but also she has given you a good suggestioon...to get professional help. she may realize she cannot help you in the way that you need right now. she cared enough to tell you what she thought would help you.
hope you will keep us posted on how things go with your parents. we care about you and are here for you. you matter to us. many of us have faced the same challenges and getting help for me was the best thing i ever did for myself. my life is so much better and i don't have the depression i once had. i hope the same will happen to you. hang in there.