It is because your fiancée is still married as far as the RC church is concerned. A divorced person cannot marry in the church unless the former spouse has died.
The problem I believe you are having is confusion between annulment and divorce.
In the Catholic church annulment means that for some reason the marriage never really happened. Example: the priest was an impostor. The couple thought the man was a priest but later discover he was not. Thus, they were never married That is an annulment in the church.
In RP the government in effect allow divorce but call it annulment. A person who gets an 'annulment' in Phil through the courts is still married in the eyes of the church.
I was divorced. Thus I could not re-marry in a church. We had a garden wedding with the mayor marrying us.
