Hustler,
Guess you found your answer by now. This happened to me in the summer, sleeping with a fit girl I met in the gym. She is unhappily married with 2 kids. Never felt so guilty in my life after. When I ignored her, she kept bombarding me with more texts. SO I told her I felt so guilty to which she said it was her who should feel guilty but she was happy to carry on but I didnt want to...! She carried on messaging me for few months but in the end she got the point...never again!!!