It's just him feel guilty for not opening up and believe in Houjou for so long and think it cause her problem because she attempt to get close to him but he pushed her away due to his paranoid about him being used to get close to his brother like other girls.I may be dense, but I don't get how the conversation happening on stage relates to youta's situation.
You can see in the panel show flashback when Youta run away from her despite her attempt get to know and become closer to him but he keep pushed away for awhile back then and his conversation with her brother made him feel guilty thinking that he causing her problem around that time he tried to apologize her for that but she basically told him that he doesn't need to anymore after yesterday talkOkayish drama, nice conclusion but still think author had a dozen actually organic and better ways to do it.
"You‘re forgiven“ gave me the ick, dunno if that‘s a translation thing tho and cba looking it up.
What is there to forgive exactly? Having actual trauma? The bro doing nothing and then spying on them? Tohno reacting appropriately to her acting weird?