Dean McDermott Checks Into Rehab -- 'I Am Truly Sorry'

Dean McDermott now admits he has some big personal problems ... so he's checked himself into rehab.

A remorseful McDermott seems to be addressing reports that he cheated on Tori Spelling, saying, "I am truly sorry for the mistakes I have made and for the pain I've caused my family."

Dean kind of mysteriously adds, he's dealing with "some health and personal issues."