Yes, this action makes me more likely to think he is guilty because there would be no reason for him to kill himself if he would be proven innocent. At the same time, he should not have been able to kill himself in the courtroom. There should be more security.
She was definintely upset and angry at him, and while what she did was very wrong, it is highly likely that he did hurt her. THere is a small chance that she is just a psychopath, but the fact that women are not taken seriously about rape and sexual assult makes this less likely.
The facts of the case proved that Jeffrey Scott Jones was guilty of sexually assaulting the 13-year-old girl long before his attention-grabbing move to slit his throat. That particular action did not make him appear more guilty, but maybe spoke to his fear of going to prison for 68 years. Since the blade was very small and his injury was not life-threatening, it appeared to be more of a bid for sensationalism than a genuine suicide attempt. He may have hoped to be sent to a mental institution, but it didn't have any effect regarding his guilt.
He might have committed suicide because he was guilty and wracked with fear about what awaited him if the court decided that he was. On the other hand, he may have slit his throat because of the stress of the trial or because he believed he was going to be found guilty when he was innocent. People commit suicide for a number of reasons and it doesn't speak to either guilt or innocence.