I am so sorry for your loss... Sending my deepest condolences and prayers for your family I am sure that he was a good, kind, and loving person and I am so saddened to hear about what happened.
I just wanted to say that none of this is your fault at all! Your friend choosing to dodge birthdays, lie about studying, and ignore messages (whilst replying to the new friend) does not make her a good friend.
I understand how difficult it is as I've dealt with similar situations with people I had known for years