What signs reveal that Lieutenant Kotler is getting very close to Bruno's mother?

The signs are when bruno says he always sees them whispering together and how on his fathers birthday she walks out not realizing that brun is there and she says kurt darling your still here, im free now if you want to..... and she trails off when she sees bruno standing there. Also when bruno describes his parents argument when kotler is sent away and the way his mother acts.