Do tu think any of the characters had regrets towards anyone else in the books?

Harry Potter
I actually think there were a lot of characters that had a lot of regrets.
Harry - I think Harry regretted not trusting Severus, as tu said. I'm not saying Harry didn't have any reason to not be wary of him, but not once did he ever consider that Severus just might be a good person. Not until the facts beat him over the head with a large neon sign, anyway. I think he also regretted running off to the ministry in OotP. I think that, in some way, he blamed himself for the death of Sirius (even if it wasn't his fault.
Ron - I think Ron regretted not giving Harry the benefit of the doubt when he truly needed it - not just in DH, but that whole thing with the Tri Wizard Tournament as well. Not only did he end up being severely wrong both times in his assumptions, but he put the friendship of his friends in jeopardy because of it.
Severus - I think his would kind of be obvious but... I think he truly regretted what he'd become, and losing Lily. I think he also regretted the way he treated Harry (and the rest of his students). While he couldn't exactly praise Harry openly, he didn't need to be so petty and childish. Imagine how much easier it would have been had Harry not been so wary due to Severus' treatment of him.
Dumbledore - I think Dumbledore has the most regrets out of them all. I think he regretted not putting a stop to Voldemort when he had the chance, being tempted por the ring, causing the deaths of so many people, not being open with Harry and Severus from the beginning, and possibly even making that friendship/possible romance with Grindlewald.
Wormtail - I think he regretted betraying Lily and James. He'd done it for power and greed, but it severely backfired on him and resulted in his death.
Lupin - I think Lupin regretted not keeping his faith in Sirius and just "jumping on the bandwagon" about how he was a psycho murderer. I think he also regretted trying to run out on tonks and Teddy and I don't think it was something he did/would have truly gotten over.
Percy - I think he regretted being so greedy and power-hungry.
Draco - I think he regretted being so naive. I don't think that, when he accepted his mission, that he had any true idea of what he was supposed to do - that he would actually have to kill someone, and other people - people he cared about - were going to get hurt in the process.

Twilight
Irena - Possibly calling the Volturi out?