Dont lie, dont give away details.
99% of women dont want a guy who kisses and tells. To the same extent though its good that they know you have other women in your life. Never say exactly what happens, say you went out / stayed in and if she pushes for details of what happened just say that you dont like to kiss and tell and respect peoples privacy.
As for not having sex with her, work up to nearly having sex and then just tell her you dont want to do it tonight. Trust me, no women has had a guy say he doesnt want to f-close her when she is willing. Continue making out but dont let her have sex with you.
If you want you can make it into a game that makes a load of sexual tension, tell her that you will only have sex with her if she can keep you in the mood for a whole week, that means every day for the next 7 days she has to turn you on but you will not have sex until the 7th. Tell her you will do the same back to her but neither of you are allowed to touch yourselves or anything.
Enjoy
