Sex and sexual relations has always been a touchy subject when it comes to weyrlinghood. Neither the books nor Anne really went into depth of what could and couldn't be done as far as weyrlinghood went, and so it's left up to the games, and inevitably the weyrs to decide what is permissable and what is not.
First of all, weyrlings ICly would be too busy to pay any sort of non-platonic relationship the sort of attention that it requires, between bathing, oiling and feeding their dragons, and building the the bond and trust between them. There simply wouldn't be time, as well as considering that Weyrlings also have chores and excercises to do.
Limited romantic relationships are permitted. No sex, no public displays of affection beyond some hand holding, the occassional kiss on the cheek is okay. Thoughts and feelings of a romantic nature are to be controlled as well as possible, and blocked from your dragon's perception, as they cannot understand it. Strictly platonic relationships and feelings are fine, but any very strong emotion will confuse other young dragons and need to be controlled or blocked from the perception of younger dragons.
Like any IC rule, those that ICly break this one will be subject to IC punishments. Credits for this indepth explanation go to Darianya.
It should be noted that the ban on sex and relationships is lifted when you have had the mating flight lecture.
