
What was the lie is the question. I think this story has what we call in storytelling, an unreliable narrator (i.e.Tatsumi). All the actions of Miki are seen from his eyes and so we don't know truth from lie because it's all Tatsumi's perspective. But getting to the point, I think the lie is that she was not his sister but his lover or at least someone he liked and he wanted her to leave her husband.
(Or, I might be wrong!!!)
I think there are lot of clues suggesting this-
First clue, is the painting.
The fact that he was looking at the painting of the Beheaded John the Baptist (I have a bit of an interest in paintings and didn't know the story, so I Googled it). The story is that he was beheaded by the daughter
(Salome) of the king and the second wife. Because the wife held a grudge that John disapproved of their marriage. Ryouma tried to explain it to Tatsumi that maybe he was the sympathising with Salome but Tatsumi had gone on another tangent about beheading. He didn't catch Ryouma's point and that's what ryouma thought to himself...'that's not what...(he was trying to say).
Second clue, Tatsumi notices Miki and the woman and immediately thinks they are lovers and throughout he keeps thinking to himself that he knows Miki is lying but he is too far gone to care or see the truth.
Third clue, Miki not wanting to report it to the police and most probably that's the night he did it with her (that's why Tatsumi says the night it all started when he is referring to the woman and the child) and the husband caught on. And ripped his nails off. He would have a flimsy claim if he reported it. He most probably wanted to run away with her but she refused saying 'his heart is in the right palce'. He needed help and he wanted him out of the picture (rage and jealousy..) So he started spinning his web of lies about the past, about his sister, the mutness.
Final clue, in the home depot
When he starts talking about it and Tatsumi realises that Miki doesn't even see him. After that when he looks at the male and female couple with longing, maybe he is reminded of of what he can't be with that woman because she is with her husband and Tatsumi kisses him. I think he had a moment of clarity then. This man really loves me and his horizons broadened in the sense he thought about giving up on her and running away with Tatsumi and that's why in the end he says, it was all lies, forget it...(or he is a little devil and he knew Tatsumi wouldn't forget and wouldn't move on. He would finish the work)
P.S. also the fact that Tatsumi thinks the woman is lying, was she ever mute. This again clues us on that it was all lies.
And do I think Miki loved Tatsumi. He did and that's why he was so conflicted. One second he wanted to plan murder and another second he wanted to leave it all behind and go on a date to Disneyland. Tatsumi sure loved him. He wanted to be trapped. He knew his web of lies but was too ensnared to care. Two very warped and flawed people in love with each other and also with other people.
I came back here after a few days to process this manga and the end.
I just thought about...
Jiang Wenxu - why did he become this way in the first place/did he deserve a second chance/would he slip even if he were given a second chance (and say He Zhishu wasn't dying)
And I realised that even though Jiang Wenxu truly loved He Zhishu. And even though in the beginning his love was innocent and sweet. It turned out this way because he was inherently a selfish, self-centered and egoistic person. He should have never let He Zhishu leave home and ruin his career and family life like that. (Okay let's say that was also acceptable, there was no other way for them to be together). But look at the series of events afterwards, making Zhishu leave the job, the company that was in fact given to Zhishu. Sleeping with that boy because he wanted rough s** that Zhishu couldn't give to him because he was scared of pain. Instead of cheating, shouldn't he have talked to Zhishu about it or compromised like all people do in a relationship. Like Zhishu had done multiple times in their relationship. And I realised that even if Zhishu wasn't dying but let's say they broke up and reconciled, there were high chances that he would cheat again and behave this way. Because Jiang Wenxu's personality is the problem and if more than 10 years with a person as gentle and kind as Zhishu could still change him. Nothing would stop him from slipping again. He loved He Zhishu but it wasn't enough to overcome his personality.
Maybe Zhishu's grandmother warning wasn't because of their homosexual relationship only but also because she had reservations about Wenxu as a person
Should they have been together at the end at least in He Zhishu's last moments?
I see this from He Zhishu's point of view. I feel like it was the right thing to not meet Jiang Wenxu in the end. He won't be able to let go of this relationship even in death. This relationship that had become like a chain round his neck which suffocated him but at the same time without it, he felt lost. Zhishu didn't really need to know that he could get back his old Wenxu. Getting him back just because he was dying would have just been a pitiful love for Zhishu. Their love was already too tainted to recover from. Wenxu had hurt him too much. He would never be able to whole heartedly trust or believe him anyway.
Therefore, his last sentence makes so much sense. Because Zhishu gave up everything for the young Wenxu. That innocent boy who once loved him wholeheartedly. The love which gave him so much joy. He wanted to go back to those times, to that love.
Also, knowing Zhishu, he most probably wanted to do a last kindness towards Wenxu hoping he would be able to move on.
In the end, I am sad yet satisfied with how it ended.
And who knows maybe, in the next life Wenxu will do the right thing and he will one day get to grow old with Zhishu having lived a life full of love and warmth.