How likely is this marriage to last? I'm in America he's in Ghana? Will he be faithful?

It depends on the length of your physical separation. If you are only going to be physically separated for a few weeks, I don't see any reason for infidelity, and your marriage could last a lifetime. However, if your intention is to be separated for years, that's not really much of a marriage, and I wouldn't be surprised if he strayed away.