No I would not be paying for the wedding. Sounds to me like they are both to young and have trust issues.
I personally would tell them live together for 12/18 months. If all well I will pay but not before.
I have used gumption for years. It reminds me of the Trusol paste we had when I was a kid. My job was to clean the bath and basin. Trusol or Ajax powdered were the only things Mum used.