Husband sex drive declining more and more

This is a hard post for me to make because I feel like a lot people will judge the things my husband did in his past and he's pretty ashamed of a lot of it. If you're going to be mean please don't comment.

My husband's sex drive has declined a lot as the years have gone. It's not bothering me too much because we are intimate in other ways. We have sex maybe once a month. What I'm worried about is his sex drive used to be out of this world. He was having sex at a very young age. He told me he lost his virginity at 11 to a 16 year old girl (I know that's gross and illegal). But he's always been sexual. He's bi so he was also very sexual with guys. He kissed his first male when he was 8. When he was 14 he got involved with some people he should not have and was having sex for money. Was also on drug for years but overall. With all of that hes always been very sexually. He willingly entered the porn industry when he was 18 and I'm saying this because I know it's not a porn addiction because he doesn't watch porn. He was in the industry for 8 years and it because he experienced so much trauma from the situations he was in he can not watch porn because it brings back bad memories. Point is his entire life he's been a sexual person and I would say the last year his sex drive has went down more and more. I guess I'm just curious on why that could be. I'm worried maybe I'm becoming less attractive. He is very content with his sex drive. Its not necessarily that I need more sex. It's just he's always been so sexual and now it seems like he's not anymore and should I be worried?

@Chantelle we've been together several years now. His sex drive started going down a year ago and while yes he's bi he's female leaning. He's dated 2 guys ever and has mainly dated women.

Edit: For my husband's age. He's about to be 40(Even though he doesn't look it at all. He looks early 30's) but maybe it's age? Is 40 when all that starts happening?

@Mommaof4 Maybe. He did start with a new therapist a little over a year ago and his sex drive has started going down the last year