I think the comments made by others here are kind of
harsh.
Cliff, i thought about this issue too. And yes, it's a big big deal
for me.
i honor ur decision to have your 'first time' only with ur lawful
wed.
But the image that plays in ur head is one thing which is so hard
to erase, i agree.....
It's so easy to claim that Love could overcome everything and all
could be pardoned. The law of Cause and Effect still stands as long
as we live. The fact doesn't change. (Will come back to this in the
latter)
In this case...you find it impossible to leave it behind.
We also can understand that subconsiously...the thought is there,
the pre-concieved nature of the person will be instilled so deeply.
To an extend 180 degree change in your approach to wards
her....responding and seeing the other party in another light.
Negatively speaking.
I'm sorry that all this have to happen. 
Advice:
Let's get real and not be noble.
-To claim that you really love that person therefore you will
accept her....this doesn't work for your case.
You love her(i see that). That's why you're hurt, not only that
you're betrayed over your 'unfailing' love towards her...but also
your belief(of saying no to PMS), ego, and pride.
It's no longer all about you...nor is it all about her.
It's about the Both of U!
To simply put across this.
'Are you willing to walk this journey with her seeking to heal one
another's wound?' It takes more then love to answer it. It takes
commitment and undying determination to go thru. Ultimately...it
takes two wounded hearts to say "yes, i'll go thru this with
you...for better or worse....i'll be there for you'
And seriously, it takes a healing hand to close both your wounds
(possibily God) 
I'll come back to the facts....it doesn't change, it cannot change.
WW and WW II won't change....neither can it. The hurts and pain
thru those pain can't change....and nor can it.
But Mindsets change....you still can make things
happen the way you want it.
The power to change comes not from others...not from God, cos the
ability of making each decisions that leads to changes IS in
you.
If only you choose not to look onto darkness and despair, look for
an answer within yourself. Note:
You are the only person who has the key to unlock your
heart.
I'll stop here and leave the rest to your heart.
PM me if you need help....