Jean remembers the mission to save Eren from Reiner and Bertholdt. A lot of people died. A lot of people died when they rescued him from Reiss too, but it wasn't from 'their people'. A lot of people also died in Shiganshina, even if Jean hadn't seen it for himself.

Compared to the weight Eren must be feeling, just screwing himself over seemed pathetic to mourn about.

Not that it made any sense to compare.

"I can never understand the weight you're feeling. But I already feel bad enough for breaking my promise to Mikasa. That I'd never leave her or go where she can't follow... so I would probably break down with even a small part of your pain."