I think people are forgetting Sunao and Lemon grew up together. Doesn't matter if he believes she cheated on him. He knows her a little too well to not treat her like a human being.
That's what i was going with b4, i was assuming most of their interactions were driven by "habit", but Sunao not going "you cheated on me with 3 guys" when she was going on about the stuff she has done for him is kinda weird, specially considering the manga didn't present him as being over all that stuff, it even emphasized on how it was still weighting over him.
Lemon being unable to come clean with Sunao is actually consistent with her character. Telling the truth would me she would likely have to also reveal that she still loves Sunao for it to make sense in context. That's a pretty hard conversation to have.
It is true that it would be a really awkward conversation but don't you think he deserves that much? ik it'd be hard for her since in this weird situation she's getting a chance to "get him back", if she exposes herself she'd be risking a lot in some ways.
Yet he exposed himself to her and she destroyed him, its unfair to think its justified for her to have ignored him for 3 years and feel no need to rush telling him the truth now. It may be understandable to some degree but not justified.
Tbf i don't think she's a bad person, anyone makes mistakes and all that, but... clean up your shit would you?
Something what does annoy me about her is how she doesn't seem to consider how he feels, correct me and maybe we can discuss a bit further but... has it ever seem like she's trying to figure out how he's been doing after her lie? It really feels like she's ignoring it at the best of her ability.
If nothing else i do think she's self-centered, not a bad person but so far she seems that way. Well maybe mc is like that as well and this is just an authors issue.
It would be cool if the manga went about her noticing how much she hurt him, plus the lowkey hypocrisy of wanting to become a better person while maybe willingly ignoring what she did to him. Then mc noticing how he's cut from the same cloth, this is just speculation and it has its own issues but it wouldn't surprise me if he hadn't noticed how bad it was for her to be a pushover... Altho then i would have to wonder wtf they liked each other, it would seem like their relationship consisted in not giving a shit about each others situation XD