Please note my answer has been updated for another disqualification as well as a note regarding how to handle a situation where the boyfriend has already claimed the child and what would be expected of you both when the IRS questions you both claiming the child.
Just to note, the additional qualification is another rule for a qualifying relative. If you are claiming a dependent as a qualifying relative and they are not related to you, they must have lived with you the entire year. This is not agreeable to a joint custody situation.
