Having an affair with my sisters husband

I need everybodys opinion, i am married for 10 years i am 43 but look in my early thirties, i take care of myself i consider myself very atractive,the problem is i am no longer atractive to my husband we rarely have sex he is always tire for me and whenever we do have it he only satisfied himself,well i dont know how but my sisters husband started telling me how much he cares for me and that he can supply all my needs even my sexual needs that according to him i was needing soo much , at first i didnt even wanted to talk to him when he told me that but after talking with him over the phone a coulpe of weeks i started liking what he was telling me about how sexy i was hr dodnt understand how my husband didnt want me and stuff,but the point is that he convinced me of having sex with him, and now we r having an affair of two weeks i like the sex but i feel really bad fir my sister, i need advices.