ForgottenLife
It's your story and side stories are a part of what's make a story, it's necessary to build the personality of a character other than the MC. Those who are complaining doesn't understand the utility of a side story and only want a diary like journey. They are complaining about side story but still do side quest on a game... You must change your story to please everyone because it's impossible and there will always be someone who complains aboit something. People needs to understand that forcing someone to do something they don't want to do destroy their passion. So you need to stand up and do what you want because even if you lose 10 readers you'll gain many more by being consistent.
The side story was not bad, even very good. But she's exactly what a side story. Side stories don't reveal enough characters to empathize with them. And most importantly, why such "long" side stories are needed when there is a main story that is interesting to read, but you have to wait for new chapters for a long time because of side story?