I feel like Tabby and Fred would have a "situationship" going on while she was living at the Brotherhood house and makes it everyone else's problem. I think she would have kind of tried with all of them at one point bc she likes to mess around, but Lance is taken, Todd doesn't brush his teeth, and Pietro, well... had a whole thing with that where she came onto him and he wasn't interested and she would have clocked him and he panicked and kissed her but she knew he was not interested and left it at that.
But yeah, her and Fred were regulars and I'm sure she would have been ok with doing stuff as long as he doesn't fall in love with her and he's sadly so desperate for someone's affection that he'd go along with it anyway. Idk if they would have stayed together in the end or not. Probably not. But they were make out buddies. Think she has a thing for big dudes anyway.
Anyway, should have said what room, Pietro! Even if he cleans the room after he'll never be clean of the knowledge that they were in there.....