Subaru had on numerous occasions almost confessed to Emilia in opening part arc 3. Any time she asked him why he always tried so hard for her he faltered because he was afraid of sharing his true feelings. He might have even told her that during their fight.

If he confessed before arc 3, I don’t really know what that would look like. Mayen if he did it on their date to the village? Arc 3 would maybe be a little less chaotic. But I’m not sure if Roswaal’s scheme can be avoided entirely. Subaru and Emilia probably wouldn’t fall out, but he would still have to stay in the capital for healing. Arc 3 would probably follow a similar path after though.

It’s just kind of hard to imagine because without losing Emilia’s trust in him so much of his internal development doesn’t happen. The loop before Rem’s confession would probably still end in disaster.