The best thing he can do, without admitting guilt, is to tell her to get on with her life, that he's not going to marry her.
He may have already done so, I think that he told his parents to forget him. His fiancee may be having a hard time accepting that the rest of her life that she was about to embark is over.
I can understand what she is going through. While she hasn't lost a loved one to death, she has lost him. Grieving is a process. Denial is usually the first stage of that process. I don't think that it would be unusual for her to remain in denial until the trial is over, because until the judge reads the verdict she can hold onto the hope that this is all a horrible mistake.
For her sake I hope that she will move on before the verdict is read. And there is hope that could happen. While she is in denial, I doubt that many of her friends and family are to. The evidence against him is quite damning. Hopefully they will help her move on. Even if my some miracle he is found innocent I think those same people will do everything in their power to keep PM out of her life.
Of course he may be prone to being melodramatic. And the declaration is a part of "coming down" from the high. Considering his lab partners comment that he had mood swings it is possible that he frequently employs this tactic to manipulated others. I really get the feeling that the suicide attempt was done so people will feel sorry for him. I wouldn't be surprised if his arrogance is so great he actually thinks that he can get out of it.
But if he told his parents to forget about him you would think that she would see that he is basically admitting that he is guilty and believes that he is going to be in prison for quite some time.
BTW, is the prosecution allowed to use the "forget about me" declaration against him? That statement really does sound like an admission of guilt to me. I can't think of anyway that the defense could "spin" that in PM's favor.
Also, has anyone seen anything that says that the fiancee has visited PM?
