There are 364 other days in the year to celebrate & socialize.
Not with " worldly" people you won't. That is most definitely not ok. You are expected to keep association with non-Jws to the minimum. Essentially work and school. The 2016 " wife of lot" convention videos even condemned associating with non-jw FAMILY. Visiting a brother, even AFTER celebrations are done, on his birthday would be a huge no-no.
Also your school analogy, comparing the need for rules with that of rules within cults, was way off the Mark. Basically a cult is an abuser and CAN be best compared with an abusive partner. A school is a place which benefits you in the end, the rules there to help you achieve your positive outcome can be compared to the' rules' within a healthy relationship - honesty equality, fairness including sharing financial burdens, commitment, respect, unconditional love.
The rules within a cult, an unhealthy place that does not benefit you, and their rules can best be compared to the 'rules' within an abusive relationship - lies, deception, extreme hierarchy and inequality, unfair burdens, financial dishonesty, one sided commitment, violence towards spouse & kids acceptable, love conditional on your obedience.