He did the right thing by rejecting Syr, Bell is too kind & honest to start a relationship with a girl while he's still chasing after Ais.
But maybe his methode of rejection could have been better. I mean he just rejected her, let her go alone while he is too busy being deject by himself & MS 17 happen. It makes wonder what would have happened if Bell hadn't let her go & had fully expressed his feelings until Syr realized just how much Bell is also broken by this decision.