
He got so depressed that leads him to have hallucinations about Kise showing up wherever he is. He was kind of unstable mentally thinking that Kise is just around him. After Kise died, he wasn't able to go to Kise's wake because he was still kind of in denial about his death but then I think Momoi and some others persuaded him to see Kise for the last time. Eventually he managed to accept the truth and let go. I think it was because he was so hung up to Kise that he wasn't able to achieve peace within himself. The end was stil bittersweet, with Aomine visiting Kise's tomb and telling him how he feels. I think it's better if you read it. It's really beautiful and I have cried buckets. If you want I will provide the link.

Here's my page. I have two AoKise fics there. I hope you'll like them. :)
https://www.fanfiction.net/~addyliciousyaoi
I have read an AoKise fanfic with almost the same story line except that the story ended up with Kise dead. I was really kind of afraid to see the end because something nags me that this will end in tragedy which will definitely break my heart. Up until the last page my heart was really afraid of what's to come because a single panel can kill Kise right away and thank goodness it isn't. Gosh, this is really beautiful.