Re: nerves, stress, unsure!
There nothing wrong in telling a small lie if it can save the family from a disaster… these things usually happen in desi culture where boys when asked by their parents about their marriage identify a girl from their friends circle for their family to consider as a prospective bride and then they send the rishta (I think its not actually a lie but hiding the WHOLE truth)… of course I dun know your level of involvement in the guy, have you been going out alot, do your friends know about you two etc etc… if yes, these can make things difficult… coz if you had already known about your family’s values and that they would not like the dating stuff even if it leads to marriage, you shud NOT have been dating the guy in the first place 
My idea is that in order to make things less complex for urself, you can say that u considered him just a friend and did not know that he started to think about the marriage thing.. as soon as u knew, u asked him to use the proper channel ONLY… u might need to discuss this with the guy… ur family cannot ever catch u for this unless and untill they find from any of the people/ ur friends or found some “pics” of u two taken during the time of dating… so its only u who knows the reality and only u can decide how to break the news to ur mum/ family…