I feel like in the last timeline Oberon probably had an idea of Yuno's plan and wanted to break off his and Capella's engagement to try and protect her. From what we see now, it seems like he truly cherished her. I can see why he would choose the breakup route instead of telling her about Yuno. Capella is very loyal to Yuno, so telling the MC that the saintess is evil would just lead nowhere. Separating himself was probably his best attempt to protect her from being used by Yuno. Unfortunately, he was too late.
I feel like in the last timeline Oberon probably had an idea of Yuno's plan and wanted to break off his and Capella's engagement to try and protect her. From what we see now, it seems like he truly cherished her. I can see why he would choose the breakup route instead of telling her about Yuno. Capella is very loyal to Yuno, so telling the MC that the saintess is evil would just lead nowhere. Separating himself was probably his best attempt to protect her from being used by Yuno. Unfortunately, he was too late.