You have not stated whether you are using condoms or not. It is better to use special condoms that claim to delay ejaculation, if at all required though there are better methods of sorting out the problem of mis-timed orgasm wrongly called pre-mature ejaculation. Furthermore long term use of xylocaine (or similar other agents) can cause erythema and pigmentation of the mucous membrane of the vagina and penis. No long term clinical trials on the safety of topical use of lignocaine on mucous membranes have been done.