Welcome!
Unfortunately for the vast majority of JWs, friendships are conditional. Conditional that you are a faithful, zealous JW. Once you speak your mind or act independant of the Society's teachings, they'll pull away from you. Over time, it's as if you never existed.
As for the convention, I don't if there was a part on distancing those who aren't progressing in their study (though from time to time they'll make it a point to remind everyone not to waste too much time on someone not "progressing"). But I did hear that they were pretty hard on making sure that the dubs followed the rules as far as how to treat DFd ones and even inactive ones. It could be that since you're not getting baptized and you question some core teachings, your so-called "friend" has decided to apply that counsel to the relationship with you and is seeking to end that friendship.
Don't feel like the Lone Ranger though...it's happened to most of us...