International Law Issues: Marriage Between U.S. Citizen and Venezuelan Citizen

I am in a very long distance relationship with a Venezuelan man. We met in Venezuela in 2011 and have continued our relationship, and now are at the point of wanting to get engaged and married as soon as possible. He currently is living in Colombia, and I am living in the United States. He has tried twice to come to the U.S. on a student visa, but was denied as the government presumed that he might plan to stay illegally in the U.S. He is now in the process of applying for an R1 religious worker visa, but we have already been waiting 6 months to receive an answer and still do not know if it will be approved. He has no plans to ever live in the United States permanently. He only desires to be here to work for a short time, as well as learn more about my culture and family. We would like to go ahead and get engaged while we wait on the answer for the visa, but we wonder if that might cause problems with the visa being accepted. Do we have to wait to get engaged until after we find out if he can or cannot receive the R1 visa? We do not plan on misusing the R1 visa for the purpose of getting married, but our relationship is progressing at the same time that this visa is being processed. We would like to know if we have to put our relationship on hold while we wait for the visa.
The other option we have is to get engaged and married in Colombia. But we don't know if we still have to wait on news about the R1 visa before making this decision. And if we were to get married in Colombia, would our marriage provide the way for him to be able to visit the U.S.? Again, he does NOT desire to live in the U.S. He only desires to be able to visit more freely. We plan to live in Colombia after marriage.

Any answers would be very helpful. Thank you in advance!

International Law Issues: Marriage Between U.S. Citizen and Venezuelan Citizen