I guess you wouldnt be posting here unless you thought it was serious and more than a developmental phase but:
Over this Christmas I am living with 4 teenagers, so please remember when it comes to this age group it goes with the territory. I teach this age group and my god they are so forgetful. My 10 year old is all organised but I can see what is ahead and somehow in teenage years they regress memory wise. It is a well known thing.
But I have to say it must have been impossibly hard for him to hear that his father didnt want to be part of his life. I have some divorced friends and usualy around this age the boys like to see a lot of their father. Is their any way they could spend more time together?
I have another question - is there a reason why you chose the Bipolar forum to pose this question in? other behaviours?
Welcome to the forums.
None of us are doctors so any advice we can give you is laymans terms and experience but it sounds to me like something that a psychologist or therapist may be able to help you with as a first attempt - yes he has been shutting out as a coping mechanism and thats also a good answer for the forgetfulness and concentration which can also be components of depression.
Its kind of hard to tell if there is anything there as we don't know anything more, I would ask you a question - was the breakup of your relationship with his father acrimonious ? Is there ongoing animosity and negativity with regards to his father or his fathers behaviour?
Children pick up on thing far easier than we think and they are very good at emotions.
I would not be worried this is short term memory loss, I suspect he is just not interested in paying attention right now and particularly to adults.
You also don't state how old he is? Boys who lose their fathers can go through a lot or stuff - mine spent most of my life working away from home and our relationship is still not normal in any way - if he has just lost his father then he will be suffering a form of grief (yes he did not die but it is grief just the same) and seperation anxiety.
I think the very first thing you should do is speak to your doctor, get a referral to a child psychologist and let the child have a few sessions with them - and then be willing to accept and understand what comes out of those sessions as well which is important.
Relationship breakups are hard on kids, there is no doubt about it and it stands to reason he is going to block out the bad stuff about his dad.