[Berating himself for not being able to keep his promise to her? He deserves it. But it hurts a lot worse hearing Monika pointing out his promise to her.

For a moment, he's stumped for words, trying to find the right words to say to Monika in this situation and failing.]

It... Wasn't my fault that I was gone. I did not have a choice. Nor did I know I was gone for that long.

[Seeing Monika turns her head away, his hand reaches out to her, but ultimately draws it back to his side.]

But... I am sorry. For... The hurt I've caused.

[He still doesn't blame himself for his own disappearance, but he can't deny that Monika must've been hurting because of his disappearance.]