He doesn’t want sex anymore?????!!!

Need advice… what to do??
We have been together 1 year. I’m 53 and he is 56. Both in good health. Have had a very satisfying sex life up until a few months ago.
In April he took a job in my area (he does construction) and I let him stay with me in my home. To help him out and as a trial for a permanent living situation.
Everything is GREAT! Except he has no interest in sex anymore. He is affectionate (tells me he loves me all the time) spends lots of time with me, helps out financially, has been doing upgrades/repairs to my home in the evenings and weekends (that he says are for us), and talks that he would like our new living arrangement to be permanent. But at night he falls into bed, complaining that his shoulder or some body part is bothering him and that he’s exhausted. He has a very physically demanding job, but even on the weekends he has no interest in being physical. I have discussed this with him and he says it’s just his job that is making him tired and the pain in his shoulder is killing his sex drive. I don’t know that I believe that….. any advice would be appreciated.