i'd take her for ANYTHING cause they're very cute, but ideally i'd like something meaty and complex, so either a major ex, someone that he had a no doubt-esque band experience where they played and created together for years and she eventually left the band to pursue her own stuff which could be a potentially dramatic line because he would be super hurt by that but eventually come to accept it cause he eventually found his own way, a childhood best friend, OR and i know this is kind of a weird one, but the little girl he used to babysit all grown up and he's still imagining her freckled and in pigtails at 12 and she's a bombshell now for some awkward cuteness. it kind of depends on what you'd want to do with her.
sorry for the c/p but those are the options i have thought up off the bat, i'm open to creating something together or skewing any of those ideas either way you'd be interested tbh