My son live in Somerville, MA (Boston) doesn't own a car, his social life is just fine. I have spent time with him and his friends, we walk to the local pubs for trivia nights, beer and general fun. Sometimes a group will get together and take the T (with people joining the group at different stops) to a museum or art show. Or just meet at the venue. The same group was headed out for a 13 mile bike ride down the Minuteman trail this past weekend. Doesn't seem to be crimping his style at all.

I dated for quite a few years while car free and had no issues, and the area I lived in at the time had no mass transit.

Aaron