Even marriage to a US citizen does not immediately convey permanent residency to the spouse. Although there is not a wait for a visa from a quota, there is still processing time during which he will need to remain outside the US.

Some may tell you that it is possible to enter on a tourist visa and apply for adjustment of status/ You have announced on a public forum that your fiance intends to immigrate therefore stating that there is no intent to immigrate would be a lie. Rule 1: DO NOT LIE TO US IMMIGRATION.

Speak with an immigration attorney. Also, you need to become familiar with the financial responsibilities of sponsorship which survive even a failed relationship.