You cannot just give a cover letter stating purpose tourism. Where were you staying ? Did you buy the airticket? If so where was your flight intinerary? Did you put in any evidence
about your work, bank statements, payslips. Evidence of strong ties to India and your home.
Appealing is a waste of time as there is no cohesive system for appealing, some countries the appeals are never answered.
It is extremely difficult for single men from poor countries to be granted a visa.
All you can do is you reapply. By the way was your fiance granted a visa?