Hi
@type1don454647, As
@Antje77 says, the physical mechanism (for want of a better word) would appear to be intact.
So it may be the psychological issue of performing sex with a partner which needs addressing. There are countless books, tapes/CDs etc. Your local library may have some. See whether there is a section on performance/performance anxiety etc (i am not stating a diagnosis just whereabouts the help you need might be found).
You, and perhaps your partner, seeing a sex counsellor is another option.
Plenty of sleep and limiting late nights, some exercise, keeping BSLs under control, no or little alcohol all might all help.
Best Wishes. Feedback of success in the form of a thumbs up is sufficient detail !!!