Bf's ex

Do any of you have trouble with ur boyfriends ex? My bf's ex just moved back from Texas and when she was gone he was really relaxed...even though he was only going to see his daughter on holidays and during the summer he accepted that...now she's back...she's been back for three days and I can already tell the difference in his stress level and attitude...as far as exs go she's crazy...absolutely nuts...I just need some help on how to help him...