Firstly this is not a romantic relationship. This is a work environment situation.
Periods of flatly ignoring everyone.
Being very frosty if approached. Even by more senior staff.
Suddenly snapping out of it as if nothing has happened.
Being quite rude and arrogant to very benign colleague.
Sweary abusive outbursts toward close friends.
Selective ignoring of some team members whilst laughing at joking with others.
Sulking or flouncing home at unwelcome news - think change of staff not redundancy or loss of income etc.
Sometimes making quite hurtful comments.
Thoughts please?