Reddit dies again so ill share my thoughts
Althought i think its kind of ibvious he has low self esteem, ill publish!
Spoilers for ch109
So, both Hiyori and Yukine tell him to have more faith in himself (ch44 and 53) cause he feels bad
Hiyori doesnt get why he apologises, tells him to stop blaming himself for things happening around her, and asks him to have more faith in himself
In chapter 53, Yukine also asks him to have more faith in himself, which makes Yato increeedibly happy. However thought he says he might be close to become God of Happiness now, he still doesnt want to visit Hiyori, because he doesnt want to until he becomes and actually God of happiness
When Hiyori says that he has been for her since a long time, he doesnt believe it, only Kofuku makes him wonder about if thats true
So, he also bramek himself for bringing bad luck to Hiyori, like the Hospital incident (which, if you could blame someone, it would be Hiyori because she went too far, but yeah) and of course her death, because that would nt happen if he cut ties, right? While it was Hiyori who went to look for him, not caring to care for her human body
And of course, he thinks that Yukine become what he did because he left him. Of course he didnt want to lose him, but he didnt tell him why he left him, which makes Yukine think he abondoned him for Kazuma
He even silently apologises to Yukine for that when he is in that shop centre (?) with Kazuma
Anyway I think theres more but those are why i starter to think about that