Boyfriend lying about his ex being his cousin

So ladies I think my man is lying about his ex being his cousin...oldest trick in the book. My problem is that he text this girl pretty often..I kinda found out he was lying by practically stumbling on some data on his computer and seeing that this girl is his ex. My question is how do I bring it up and tell him I know that she's not his cousin? I really don't know why he's lying though...🤔🤔🤔 ideas ladies..please