A lot of things can make this happen. It doesn’t mean she’s not physically attracted to you. It could be she’s not interested in sex for some reason or other. She’s not attracted to you because of relationship problems or personality mismatches (that happened to me when I found out I was dating a too submissive man who was pretending otherwise once), or (more rarely) she’s not physically attracted to you.
I say more rarely because if you’re a long term married couple it’s doubtful this is the case unless you had a drastic appearance change, she “settled” for you and was never attracted to you to begin with, or if it happened right after the honeymoon stage when NRE left.