Oligodendroglioma

I have a friend who was just diagnosed with an oligodendroglioma-stage 2.  The doctor said it was not cancer.  Is this true?  From what I've read, it's just slow growing.

He is starting radiation this week and will go 5 days a week for 6 weeks. The doctor mentioned chemo after radiation but said that chemo has not proven very effective with this type of tumor.  Is this true?

In my opinion, he has had major personality changes. He doesn't really see that. He knows he's struggling with memory, reading, writing, finding the right words to say, etc. but doesn't see anything else.  We have been best friends, very close, for the past 6 years. Now, he is pushing me away. He doesn't answer my phone calls, texts, etc. but will call if he needs something (like for me to take him to radiation or to go buy his meds). I'm very upset, lonely, angry and frustrated with this. Is it all the tumor, or is he just being a jerk?  He's pushing his family away too.

I don't know the best way to support and encourage him.  

He is struggling with reading, writing, speaking, memory, attention and anxiety. Is it "too early" to do any therapy or activities to help him?

I know I've posted a lot of questions, but I'm limited on who I can talk to. He doesn't understand/remember things the doctors tell him. I was taking him to all appointments and keeping up with his medical information and records, but now I'm not.

Thanks!