Is my son acting this way due to the loss of his father?

Times have been a little rough in our family this year, and it resulted in the divorce of my husband and I. He moved out and never said a word to me, my daughter, or my thirteen-year old son. Ever since he left us, my son has been acting very strange. He comes home three to four hours after his school bus drops him off, his teachers have been emailing me about incidents with other students, and he has chosen to walk out wearing all black and gruesome designs on his shirts. He also is very strange at home. My daughter comes to me every day saying, "Mom, Tommy is trying to get on me!" And she is only eleven. He apparently has a new "attraction" to her. Is this all from the loss of his father? They weren't very close, yet he seems so distressed.