every guy is different, people are usually into different thing, maybe he just realized he's into transe sex and he doesn't want to tell you about it cus he is ashamed, or that's his way of telling you he is no longer into you
Dropping down to sex every 2 wks w/in 6 months isn`t a good sign. He may be bi-sexual or maybe he`s still trying to figure out where he`s at sexually himself. Six months is a very short time. If it were me, I`d have a very serious talk w/him & if u don`t like what you`re hearing, move on. It`s your life. Don`t waste your time.
You can be the best judge in this regard. you create a situation where you can have a frank talk and renew the relationship or terminate the relationship. It is only 6 months. It would be getting more difficult to judge his as the time passes. However you have a further guidance from other members who are expert....