Have you taken into account how you’re acting? Perhaps you’ve been cold towards him recently, causing him to back off a bit. If it’s been going on awhile just confront them politely and ask what’s up. Do not accuse him of anything, just say it feels like X, because Y- or something to the similar effect. I use to be really lovey and text/talk at every opportunity with my girlfriend (with little to no reciprocation most of the time) but she didn’t seem to really appreciate it so I backed off; you don’t really tell us much about the situation, but just take into account that your actions have effects on others’.
(I’m not trying to blame you or anything but the way you phrased your question implies you’re looking solely at him as the cause/reason for your discontent)