Men over 40 Sex

My husband and I have been struggling with our sex life. His libido has gradually declined and especially in the last year. I noticed him buying "steel libido" but never admitted that he was having a problem. I would ask him what the problem is but he never confessed till now. He says he has low libido due to work stress and age. He mentioned the steel libido (vitamin) but forgets to take it. So my question for you ladies (or men) Is there a

Non prescription vitamin that your lover takes? How do you remind your partner to take vitamins? How do deal with partner of low sex drive and yours is higher?

Thanks in advance for your suggestions or ideas!