That's what I'm hoping for Ren too.
you can love two person at the same time. I just feel like this theory about Ren being reborn as Arata makes sense. It may not be Ren's initial goal to participate for the experiment initially. But he knows what it will do to Maki. He knows that Maki knew he was just a substitute for his brother. As their relationship went on, Ren may actually feel something for Maki. Ren has been loving Maki's brother for the longest time. If Maki and Ren were given more time together, pretty sure there will come a day where Ren's priority and feelings will be more for Maki. And I think that's where Arata completes everything eventhough technically he's not Ren. He's like part of Ren. It's interesting to note that even after the imprinting Arata still loves him which maybe solidify the fact that Ren might have already developed certain amount of feelings for Maki
Saying sorry to someone means you care about the person. That person held something for you be it a little or more.
After rereading this for countless times, I started to think about Ren.
Yup, he sounds like a very cruel person to Maki here, but somehow I began to think that that's not everything. Ren did loved Maki's brother, but maybe(just maybe) he started to have feelings for Maki, and started to feel bad for Maki.
However he feels bad that he still cannot forget Maki's brother, and cannot forgive himself for what he had done to Maki, and decided to get his memory taken so that even if he died, the reborn Ren (Arata) can love Maki with all his might.
Anyway, this is just how I think. Surely Zaria sensei knows better.
I still hope that one day Zaria sensei can make a special chapter of Ren's story.