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... she has joined a sorority and since then has been incredibly secretive and very ready to reaffirm her love for me, which has begun to make me a little bit suspicious...

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You sound a little paranoid and insecure at the moment. I would caution you not to go jumping to conclusions. If I were you I'd just focus on the fact that she is in love with you and I'd be excited about that, not go looking for reasons to want to dump her. Look forward not backwards. Two years is a long time and your relationship with her is clearly very important to you so don't go screwing it up with your insecurities and your imaginations that she's lied. Once you start thinking this way you'll never stop seeing the evidence of it.