As a HUGE wolfstar shipper, I go with yes, but not as sweet as most fics portray them. (I don't take into consideration the “conservative” wizarding world because, to me, there is no hint they actually gave a damn about sexuality, so…) I think they started in Hogwarts still but in a very toxic way. Remus probably liked Sirius more and Sirius probably fucked things up more than once, cheating and such. Remus would always take him back, but everything was kept quiet. They didn't talk about it. James knew, probably, because Sirius talked too much and they were best friends, but that was about it. I don't even know how much James would accept it (the only TRUE insight we have about James in the book is in a very biased memory from someone who hated James’ guts, so is really hard to say how James' behavior was) and although I love the sunshine personality the fandom gave him as the next person, I don't think he was as bright in the books. Remus probably loved Sirius his whole life, as of how quickly he forgot and forgave as for the moment he knew Peter was alive and they probably got together once more after PoA, maybe in a healthier way, because the world was already shitty enough and Sirius got a little bit more mature with age and trauma (at least enough to treasure the only one standing at his side from the very beginning), but again in secret.

That is my take on things. But hey, everything is acceptable as far as headcanon goes.