something fishy

I’m single asf n my bestie has a bf. I feel something kinda off with him recently, and the way he has been acting. I treat him like a brother n we wind each other up last time I seen him, in a way he was being quite flirty and ended up when I was super drunk and passed out he was giving me a snuggle during the night and chucked my bsf off the bed (I had no clue until I was made aware). We don’t keep in much contact we just see each other in person. He has been odd posting all of these private stories but they are quite bizarre something I feel my bsf wouldn’t approve of. I don’t want to read into it and make something daft of it I want to tell her but I also want to just keep an eye on it to almost protect her. Any advice ? xx