Libido I always found a variable very hard to objectively describe. You cannot really say 'today my libido is a 7' for example.
However if I look at my own behavior I see 2 things happen.
1) I find it harder to walk away from sex again. Before PFS I was one horny MF. I notice that when I flirt now, whether it is via text or face to face, that I am more determined to let it escalate into something sexy... During my PFS I literally could walk away from every sexual situation. Sometimes I really had this feeling where I felt like 'ok come on you find this hot, find it hot!'... In other words, I had to talk myself into being turned on.
2) This is going to sound very weird but my taste in women changed during my PFS time. Before I liked hot confident and sensual women. During PFS I started to become more drawn to shy kind of nerdy girls... Don't know why, probably has something to do with sexual polarity since I felt less like a man. Now I feel that the nerdy girls don't really do it for me anymore and now I am more back to my initial preference.
Hope this makes sense, had some beers.