In the beginning of S3 however the group dynamic was pretty tight and he finally starts releasing snippets. True to form he never follows up on it and flat out states that he's in trouble. The barely there reactions he gets from the others probably strenghtened him in his belief that he should just bottle it all up and deal. In fact the most extreme revelations don't come from him, but a vengeful Cordy.
There's a possibility that Cordelia was very understanding of it all when they were dating - and that was aiding in his decision to become more honest with the rest of the group. But in Xander's eyes once they'd broken up, all it turns out he'd actually done was given her ammunition to use against him should she so choose - personally I don't think that was true of Cordy, but he wouldn't be able to know the difference between what bits of information she might feel would be crossing the line to use in front of others and which bits she was simply holding back to use at a later date.
And when looking at that in regards to how he interacted with the others; Xander and Buffy often had very verbal disagreements when they had strong differing opinions on subjects, and he wasn't as close to Willow as he had been prior to the fluke... he might have seen the possibility that both of these people could also turn against him if things didn't work out as he might have wanted them too, and as a result for the rest of season 3 doesn't feel that he is as comfortable with the idea of sharing that he seemed to be earlier in the year when life did seem to be going his way. (I can't remember enough of the season offhand (even to really remember him doing any of the sharing), but did it seem apparent that he was sharing for earlier parts of the season, and then drifted off as Cordelia was the one providing information once they'd broken up..?)
Re: The one where; Xander tends to learn his lessons and learn em well
There's a possibility that Cordelia was very understanding of it all when they were dating - and that was aiding in his decision to become more honest with the rest of the group. But in Xander's eyes once they'd broken up, all it turns out he'd actually done was given her ammunition to use against him should she so choose - personally I don't think that was true of Cordy, but he wouldn't be able to know the difference between what bits of information she might feel would be crossing the line to use in front of others and which bits she was simply holding back to use at a later date.
And when looking at that in regards to how he interacted with the others; Xander and Buffy often had very verbal disagreements when they had strong differing opinions on subjects, and he wasn't as close to Willow as he had been prior to the fluke... he might have seen the possibility that both of these people could also turn against him if things didn't work out as he might have wanted them too, and as a result for the rest of season 3 doesn't feel that he is as comfortable with the idea of sharing that he seemed to be earlier in the year when life did seem to be going his way. (I can't remember enough of the season offhand (even to really remember him doing any of the sharing), but did it seem apparent that he was sharing for earlier parts of the season, and then drifted off as Cordelia was the one providing information once they'd broken up..?)
Mike C
(continued in second response)