2-3 years that's how long usually love lasts. Guess she fell out of love cause yeah - like Smackie said, the honeymoon period was over. She constantly needs to be in love or she cant work it out - relationships just don't work without being in love for her. That's often how it is with religion - 2-3 years are euphoria and then even most religious people can fall in depression.
I think you should have seen couples therapist while you both was together after second year. You didn't noticed or ignored signs and now it is too late to go to the therapist together. You can go to therapist alone just to have someone to talk with and help you move on.
Yes, you're fairly quite tough
Always having bad luck
You think you're going crazy
Look up, there's a new life waiting
Your head's buried in the sand
You're being dealt the wrong hand
Can't imagine how you feel
Only you know that it's real
Don't look back
Just carry on
Carry on
Carry on
'Cause you are stronger
Yes, you are stronger
Doubt kills more dreams than failure ever will