She easily gets jealous of any girl who he has a crush on and often times attempts to sabotage any chances he has with the other girl. Arnold and Helga do become an official couple afterwards, though likely in an effort to keep the relationship a secret at least at first , Helga continues to act mean to Arnold in public. US News.
Episodes have been dedicated to their relationship, which is the most catalytic and complicated of the series. There would've been some new characters as well, possibly Helga's extended family.