I agree with Hakphin, you are old enough to go see your parents if that is what you wish. Just because you aunt and grandmother have not forgiven him or your mother for his past does not mean that you do not have to allow this burden of hatred to weigh you down. You are doing the right thing by loving your father, imperfections and all and going to see him and be there for him. Plenty teens are not able to forgive their parents for taking away their cellphones or grounding them but you have forgiven much greater and that is tremendous!
Explain to your grandmother that you appreciate her in every way and that you love her, but as everyone else does, you have a need for your parents and that you want to be with your father through his rough time. Take care and keep posting.
Anna
You're seventeen now, not ten. If you want to see your father, then by all means go see him. The relationship you two have is between you two. Don't get me wrong, because I know where your grandmother and aunt are coming from. They're probably worried that he will be a bad influence, and there's a good possibility that he may be. This is why you need to set personal boundaries with him. A good example would be for him to be clean, and keep the dope heads away while you're there.. If he respects your wishes, then I see no issue with you talking to him. You should also set aside some time to talk to your aunt and grandmother, or if it's too hostile maybe write a letter explaining how you feel about this.
What happen with your girlfriend? You mentioned that you two have been fighting but not what it was over.
-H