It depends on what sort of social life you want. The churches have quite a thriving scene, depending on which church, of course, there are also around three nightclubs and there are other more traditional pursuits, such as choirs, Rotary, Lions and Round Table. There are also various societies, a Bridge club, and the Llandudno Extravaganza is a year-long event in preparation, so they always need people, while the existing youth groups are always looking for helpers.
So no; it's not seasonal at all, and there's plenty to do, plus you'll soon make new friends from all the groups you attend.