True love comes quietly, without banners or flashing lights.Erich Segal
Aisha and Nex didn’t fall in love quickly or dramatically. They got to know each other over time, discovered similar interests and personalities, realized they work together well, etc. Eventually, their feelings for each other became romantic.
No, this isn’t my opinion on how it happened. It’s what Rainbow intended. Nex’s character description said he would “gradually fall in love with her” (gradualmente s’innamorerà di lei), and Aisha would realize near the end of Winx season six that she “really loves him” (amarlo davvero).
In other words, Rainbow meant for this to be a normal relationship with natural development, instead of “insta-love” or the limerence-induced frenzy Hollywood calls “true love”. Some Winx fans say Aisha and Nex act like a real-life couple. Maybe that’s why.