Hillbilly has hit on the head again.
The part about giving the bride away is done by the Father of the bride or a respected male of the bride's choosing, usually a family member.
I was a bit suspicious until I read you have known him for 4 years. Assuming you have decent judge of character and are not a "pendejo" under Dominican standards, you will have done something to really enrich your life.
I had a similiar experience while I was in the Peace Corps. I helped two brothers from the campo to which I was sent, start a small solar business which has endured for 14 years now. We installed about 100 systems in the year or so we spent developing the business. After I left, they have consistently built it into a respectable income for both of them.
One of them was able to continue on and finish his Master's in letras and education and basically enter the middleclass. While visiting him on one of my trips, he pulled out his master's thesis and showed me where it was dedicated to me. I was shocked and incrediably honored. The only thing I really did was access us into the Peace Corps sponsored training, drive one of them around on my motorcycle, establish some respectablity (being a gringo has some advantages), helped in setting up relationships and lines of credit with a bank and the suppliers in the capital. The most important thing I was able to teach them was to focus on quality and service, within a few months, we got pretty good at it. I was a political science major myself so it was all new to me. They were already hardworking and incrediably honest. It was amazing to watch them grow and it didn't cost me a dime.
When this thing all started after I was sent to this campo near Castillo and lived there for three months before moving into SFM. I never paid for rent, food, or anything while I lived and worked in the community. One of the fringes of working with the rural middle class is incredibly good food and the best natural fruit juices you could imagine.
One last piece of advice, don't become his patron but be a friend. Us foreigners usually are not very good at the patron thing.