As a long time redditor, I swear I have seen this pic before.

Its true it was posted and was on the frontpage lately: https://www.reddit.com/r/OldSchoolCool/comments/4t50ij/my_girlfriend_being_the_epitome_of_cool_in_the/

But that still doesn't prove that this is "your" girlfriend in the picture. Sorry to burst your bubble but your account has no proof of pretty much anything. You could be any account copying that from reddit and posting it here as "your" girlfriend.

and re-posts on reddit are really common, at least cross-posts to different subreddits.