I highly doubt he’s autistic - I think he has been fed this narrative by his manipulative mother for them to financially benefit . The nature versus nurture argument lights up in my brain when I think if Marcus and his alleged autism.
He is clearly romanticising but very much like the way we all do over our first love , first person we felt a connection with- this male gave him attention and Marcus had clearly not had that before and immediately presumed the guy loved him for being so attentive. To be fair , the guy was probably off his chops, and an extrovert who thrived on attention off anyone.
Something intimate could have happened , but this Stephen was in some world that involved drugs and alcohol .These scenarios are very complex. I’ve been in these worlds, ‘straight’ people do cross lines , but then hop back onto being straight when the dust has settled . It’s not right , but it happens ten and plenty.
Marcus is young and not lived , he’s loooking at the situation all wrong , but I would say we have all done the same when young or met that person we really fancy , and they’re simply not into us.