My advice?
1) Validate, validate, validate
2) I think it's okay to mention that you would like to have sex more often, in a non-accusatory way. When things were bad in my R (I didn't know then that H was having an affair) I actually got H to agree to a set night of the week (he wouldn't agree to two ) in front of the counselor. That way I wouldn't feel rejected all the time. Well, I made sure those nights were really something special - and before long, even though H was still really confused and thinking he wanted a separation, there was a part of him that was thinking "gee, if I leave her, I'll never have sex this good again!".

Now, there were a LOT more factors involved in us getting back together, but the sex didn't hurt!

Good luck.
Ellie