Is it sex as a spectrum? Any sex is fine, just make the TIME with me to get all sexy? Or are we talking penis in vagina, in anus, in mouth stuff that a non-erect penis makes hard for him to execute? What are you asking of him sexually -- more TIME with you or more of a specific act or technique? (Has he seen his doctor? He's responsible for his own equipment and physical health, right? Age? Could it be andropause?)
Last, if he promised you, in my world?
He has the responsibility to follow through on a promise made. So I'd call the marker in.
And if he's not happy about that, renegotiate contract before proceeding with R. Basically, be in right relationship with YOU before adding more to the mix.