Foryou wrote...
He had no where else to turn. The templers were corning him and he was tired of running and wanted to stand up.
So he made the only decision that would prove his opponents right and completely invalidate everything he worked for up to this point. And then he attacked Hawke and his/her party, the only ones willing to stand by him (depending on your decisions).
Your defense rings hollow. Orsino might have been desperate, but I'm not going to let him get off that easily. I think it's bad writing.