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Since the GF can't undo the past, the only logical solution is acceptance on the part of the BF or, if that's not possible, the dissolution of the relationship.
BTW: if Alex really is a grad student, I'd suggest that this is just more proof that there are far too many grad students working for over-inflated degrees that bring little to the table - it doesn't take secondary education to see that the past is the past and either deal with it or move on...