Well, the main problem is that he was her first love, and with him being older than her, made her “try her best” to look adult even if she wasn’t having fun in doing things.
Love isn’t like this, that’s why she fell in love so quickly now...Aoyama is much more carefree, and also really care for her.
Really, it’s going so smoothly that I hope there would not be any drama for the main couple because it would be totally undeserved.