Responses
I think it's for both of them. The seme said he was thinking of taking Kasaragi san back until he saw the uke and he was on his mind and yes he became interested. So it's for both of their sakes. And I don't think it's such a bad thing. They found something common in their misery and I hope it turns out good. But yeah, I understand why you feel this way, that the seme's feelings aren't particularly sincere towards the uke. It's because the pace is kind of fast.
It somehow seems like the "seme" is projecting himself onto the uke. It looks as though he's trying to "save" him. But not essentially for the wellbeeing of the uke but more for his own. It's like what he thinks he would have needed for himself, and now tries to realize with the help of the uke.
I don't think the "seme" does this because he has feelings for the uke nor because he really wants to help. It seems more like he wants the uke to admit that he has been thrown away so that he can reassure himself, that he himsef doesn't love nor need the abuser anymore. For me it appears as if the "seme" himself isn't freed from the claws of their ex. (Not that that is an easy feat. Absolutely not. It takes years to get over something like that. And even then you always will carry the scars with you) It definitely isn't a heathy coping mechanism.
I really hope they learn to love again. Not necessarily romantically, more that they learn what "Love" really means.
I hope that they learn to love themeselves.