If this is your first relationship since splitting up with the lady who cheated on you, then is possible that this new relationship is a rebound affair?...something you have gone into because on some level you know there is no real risk that you will fall for her and be hurt all over again?
I read somewhere that some people need to have a purely sexual relationship in order to heal their broken hearts and be ready to love again...others need to love another person but not have sex with them in order to heal and know they are ready for the same. It may seem like an odd concept, but it seems to me that most people I know do one or the other for a time after they split up with someone who was important to them.
If neither of these scenarios fit what you know about yourself, then maybe your libido is affected because you are still grieving over your last relationship and simply haven't got enough energy to be intimate on a physical level with anyone yet....perhaps your body is sending you a message - "it's a little too close, a little too soon - I'm still feeling fragile and vulnerable emotionally to share my heart".
Just a thought, Sue. P.