I read the novel again, finished day before yesterday.
I maintain that there is no reason to consider anyone's life ruined. It's true Helga wasn't 'married off' as I remembered. It was more of a Dorothea Brook sort of thing. Anyway, she soon regretted it. She married a pastor and living with him caused her to lose her faith, surely some evidence of his hypocrisy. Anyway, she was dissatisfied with him and had no way out. She says that her 'duty' had always been difficult. It is only 'more' difficult now. Glas, when asking why she doesn't divorce, confirms that she has independent financial means. Of course, Vollman is the exception to the rule; therefore, Helga is better off without Gregorious. And of course Helga is in despair at the end. Her lover is marrying another woman. The letter is possibly for him; it's certainly not for her dead husband.
Glas certainly feels some remorse, mostly after learning that Gregorious's mother is alive. He seems to be getting over it before the book ends though. Glas, at the end, comes to feel he has no chance with Helga. I think he has actually been quite aware of his attraction to her; I said before that he wasn't. He does delude himself in various ways though. He has apparently imagined he might be with Helga sometime.
Any comment he makes about his own feelings can be unreliable, but as this is a diary which he hides, not a confession, there is no reason to feel any reportage of events or other people's words is unreliable. Helga makes Gregorious seem pretty unpleasant. Birck and Markel also consider him a distasteful hypocrite. Glas is not alone in disliking him.