It sounds to me that your boyfriend (remember, that's all he really is at this point since he's yet to make anything official) never had the opportunity to fully "rebound" after ending his relationship with his ex-wife. You did mention that he was still sleeping with her up until the point that y'all began dating, correct? All that you're witnessing - the keeping of the piano, the "forgetfulness" that the wedding dress is in the closet, etc. are all part of the grieving process. Unhealthy? Yes, but it's reality. You're in a relationship with a man that has yet to fully grieve the end of his last relationship.