That is really weird, I don't know what might be wrong with him.
But you can try asking him, If there is nothing wrong and no problems anywhere then why did he change then?? You said your sexual life was happier earlier right? But know you are barely having any intimate time together, ya??
Ask him why is this change all of a sudden.
And do honestly tell him that, unlike him, you do find something wrong with not having sex. And that's totally normal because sex is actually the top level of love in a romantic-love relationship, and its in the human nature.
Tell him that both of you should be satisfied and you guys can find solution that satisfies both of you.
You can also do one thing, I am not sure, but it might work.
Try to act like him (meaning do not ask for sex), Control your needs and ignore any sexual desires. Act normal in everything else (eating, sleeping, laughing, the way you normally dress or talk to him etc.) I mean act completely normal in your daily activities. And just do not ask for having sex for a while (a couple of days, weeks, may be a month) and see when will he himself asks for it. And when he does just go over the issue again and tell him why did he change and how your sexual life was before and how it is now and all that (what I've told you up in this post).
I am not totally sure that these ideas might(not) work, because each person is different from the other and we never know whats inside his minds/thoughts.
I am actually just thinking with you about some strategies that MIGHT help.
Try your best if you love him :)
Let us know what happens.