Dear Harry,
It's good to hear from you again, even if the circumstances are less than favorable. I've been talking with everyone I know who might be able to help us. Dumbledore has been no help and I am not expecting anything more from him. Mum is looking into laws and spells that might be able to help us, but I'm not optimistic. I don't really know what else to say to you except train hard. I'm sure Hermione can help you with that (that girl of yours is one smart cookie).
You also asked for advice on what to do about Ron. Harry, this has been a hard letter for me to write. I have no easy answers for you, for any of your questions. I am in shock that Ron has treated you the way he has. I know he can be a bit temperamental, but this is a new low for him. If I'm being perfectly honest, I would probably cut ties with him. I know you two have been friends for years and have been through much together. However, if he doesn't stand with you in this, he would probably abandon you in other, more important things. That being said, if he genuinely apologies (and means it), then you might be able to reconnect with him.
I'm sorry this letter has been such a downer, but this is a heavy matter. Through all of this please remember that we love you and are here for you and will help you however we can. Tell Hermione we said hello and thank her from us for staying with you and supporting you (Really Harry, she is a keeper). Mum also says hello and wants you to remember to eat your vegetables. We will hopefully see you soon.
Much love,
Dad