Don't ask her about V-day, if she wants to share that with you she will. That will be a positive if she does, why make it just responses to your inquiries and presure.
You have to let your thought go about OM. You don't know any of whats going on between them and you may never. All you know is what she tells you, so why not take her on her word rather that imagining all the negative possibilites. I had and still have to with my W.
I look at it this way, if it was a friend sharing the information I would trust them until I had concrete evidence to the contrairy. Your GF is a Friend so why treat her differently. Have faith that what she is telling you is the truth, only God knows all the details.
Once you get to this point and you are open to her, and once she becomes comfortable around and talking with you again, she will start sharing the details of her day with you. It won't be everything, but you don't share everything either. Its feel will, you can't force someone to do something.
Take care, and ice that hit from my 2x4
God Bless You,
Reuben
Cautiously hopeful and keeping the Momentum
