Long Term Relationships And Sex

Not gonna lie, Steve and I are nearly four years into our relationship and my sexual drive has shifted from when we first met. Now I know this is a normal thing but I wanted to know why for two reasons. One, my, "it's too late, I'm too tired, I'm about to get my period", and so on reasons were wearing Steve down. Second, I didn't want to be nearly 35 years old and dismissing my sexual energy. I got onto an incredible book by Esther Perel, Mating In Captivity. In my opinion this is a must...