It's extremely difficult to get a visitor visa if the person does not have strong ties to the DR.
Here's a link to get all the info you need
USCIS - Visit the U.S.
As far as getting a fiancée visa is concerned, there are rules in place and you would have to get married within 3 months of your fiancée arriving in the US so unless you find someone you are planning to marry don't bother with that route.
Info on that
USCIS - How Do I Bring My Fianc(e) to the United States?