marriage

I am about to make my third trip within a year to visit my girlfriend in S.A. I told myself I have to make a decision for marriage or end the relationship. She has indicated she would like to marry me.I feel I have to make the decision because I do not want to string her along. I told her I would make the decision on my next visit.
I am not the type to make important decisions quickly. But, realize
that under these circumstances I can't keep this up for a long time.
For those who are married and engaged: Did you give yourself a time limit? Looking back now would you have done it differently?
Did you "know" you wanted to marry her on the first visit? Or on subsequent visits? If so, how many visits did it take you to decide?
I know sometimes things develop quickly for some and slowly for others. I also know from experience it is possible to wait too long and lose a good opportunity. But, I can't force myself. I have to feel at peace about it.
I thought maybe she should visit here first but I know she does not think she needs that. Plus, her parents don't like the idea of her travelling alone and I respect their decision.
For those who are engaged. How long will you wait before you get married? I look forward to all the insight