I think the best headcanon for wolfstar is that Sirius was drunk and angst and actually only came out to James because of that. Like it was really late at night in maybe fifth or sixth year and both James and Sirius have had like ... twelve to many shots of fire whisky. And at some point, between rousing choruses of Mind at Work from Hamilton and Seasons of Love from Rent, the boys start drunk talking. You know, when you start to talk about all your deepest secrets and suddenly it all comes spilling out. So James confesses his major insecurities to Sirius, not like Sirius didn't know but it's nice to know that James trusts him enough to tell him face to face, and Sirius pauses him in the middle of a quidditch self consciousness rant and just kind of blurts out; "I'm gay and I had a crush on you in third year."
And James's reaction, because he's drunk of his AAAAAAAAAAAASS, is to smile and lean in to Sirius. Sirius let's out a huuuuge sigh of relief, maybe he's not as drunk as we thought, and they fall asleep cuddled up to each other.
Cue my super insecure wolf baby walking in on the adorable scene. Now he had his suspicions about Sirius's sexuality but he figured that if Sirius was going to say anything he would do it in his own time. But seeing the two of them like that, sleeping with their faces super close together, very k-dramaesque, has his heart cracking for no apparent reason.
So he starts avoiding both of them.
He also, in his month or two of avoiding them begins to notice how coupley they act.
James is constantly pulling Sirius in for really drawn out hugs and glancing over at the other boy with a sort of soft worry in his eyes. Sirius is as playful as usual but there's something gentle in the way he looks at James. Something almost romantic.
What he doesn't see is the worry in James' eyes when he stares at Sirius' slowly thinning cheekbones. What he doesn't see is Sirius crying himself to sleep at night.
What he does see though, is Sirius sobbing in the dorm room one day during classes.
It's transfiguration in a mo' but Remus figured that was enough time to pop back to his room and grab his stuff. At first he's not sure he should talk to the boy but eventually he works up the courage to go over, because his and Sirius' friendship didn't mean nothing.
And Sirius sits their sobbing into his shoulder for the entire period.
They don't talk about it afterwards but Remus starts hanging out with everyone again. It's the gang all back together and Peter could not have been more relieved.
It's a couple weeks before they talk about it. It's a couple years, three months before graduation to be exact, that Sirius finally gives an honest response.
And their relationship takes work. It doesn't just magically start and they get whisked into a fairy tail. But it's a solid one and it lasts a long time.
And then Sirius gets sent to AzkabanZ