As a verb, use means "to put into service," "to make use of: "He will use my car today." The principal parts of use are use, used, used: "He used my car yesterday." "He has used my car for a week." When did is added to the verb phrase, however, the word should be use: "He did not use to borrow my car." When used is combined with any form of the verb be, it is followed by a verb form ending in -ing: "He was used to borrowing my car." When one wishes to express habitual action or everyday occurrence, used may correctly appear in a statement such as "He used to borrow only gasoline." Such expressions as "used to could" and "used to would" are dialectal and illiterate.
Dictionary of problem words and expressions. Harry Shaw. 1975.