What are the documents(paperwork) I need to get my boyfriend from Mauritius to the USA on a tourist visa?

My boyfriend was born and lives in Mauritius. I was born and lives in America. I have gone to visit him, his family and friends twice since 2011. We want my boyfriend to be able to come to the USA and visit my family, friends and the way of life here. This is a good time for him to visit since he is not working at this time. I have written up an invitation letter.I want to know what I need to do to get him here on a tourist visa? What paperwork is needed from me to send with the invitation? Can I marry him while he is here on a tourist visa and get to stay.