Is it just sex that he has lost interest in or is it doing anything with and hanging out with you?
Two separate issues. Do you two still hang out and have fun together and enjoy each other in non-sexual ways? Or is it that all gone also?
42 is young - but it could be testosterone issues; stress; male menopause.
When was his last physical? A check up may be in order.
How is his work? How are his stress levels? Have the household finances changed? Do you have young children at home?
Basically, has there been any significant changes to his/your life/lives in the past year?
What do the two of you do to stay connected?
Talk? Date night? Run errands? Exercise? etc.
Does he feel like he can not please you or keep up with you?
Back off from asking for sex. Let him relax about it for a bit..I know, contrary to what you want. But he knows you are not happy about your sex life. Knowing that is going to make him feel bad and associate sex with negative emotions with you. Then it all becomes a cycle that he is unable to break. So, back off....focus on enjoying his company...give him love - let him know that you love him. Strengthen the foundation that you have with him.