The forgetfulness is probably not directly related to bipolar. All of the atypical antipsychotics (Seroquel is one) can cause short term memory issues.

As for the lying, it's not likely that it is a direct symptom of bipolar. However, almost all bipolar people lie when they are manic in order to cover their trail. And by manic, I don't mean hypomanic. I mean full on, all ahead flank, 500 MPH straight toward the wall mania. It doesn't sound like he is there, so I agree with PlatinumHeart. It's not bipolar. It's just part of his personality.