Catalyst-
I've been following this thread, wanting to contribute, but a little hesitant. No matter how this situation strikes outside observers, we really can't get inside the heads of those involved. And, relationships are such important aspects of our lives, and they may be fragile and relatively easily damaged - sometimes by a single event (like an accusation, or a growing doubt).
I have now decided to add my take on this, repeating that it is just my view - based on my own experience and emotions.
Let me tell you first where I'm coming from.
I'm a 55 year old male. I was married/shacked up for 11 years - from my late 20's to early 40's. Then I was single for 14 years, now I'm married once again - this time happily. During my single/divorced period, I had a succession of relationships - quite a few, really. I'm giving you this background so you know I've been around the block a whole bunch of times - not YOUR block, to be sure, but I know the signs.
The porn is meaningless. Every male ever born in the history of the universe is stimulated by porn. Every man either has a collection or wants one. We are visual, and we like to look at naked women. That's all part of the PLAN. I think even gay guys like gay porn. It's just an aspect of our make-up.
Chat-room and internet relationships are an entirely different matter. I have to assume that these chats are not so innocent - or else, there would be no issue, no covering up, and no guilt - and from your accounts there indeed seem to be some of that. If it were innocent, you would know it intuitively. My wife knows I like porn, and she knows I post on this forum, and neither represent any threat to her what-so-ever.
Even if your SO is not planning to develop any of these internet relationships to the point of meeting them, it's a concern. He is doing something on the sly, investing his energy and emotions into other relationships, and then keeping them secret. None of this bodes well, to me.
You haven't said how old you are (or if you did, I missed it) and how much experience you have with relationships. I take it you are on the youngish side, for some reason. This could be just a passing fancy on his part, but frankly, he's acting like I remember I used to when I was withdrawing from my many relationships in my single/divorced phase. Keeping secrets about communications and pictures of cyber-companions just raises a huge RED FLAG.
It's time to have a heart-to-heart with him, and find out just where he's headed. If you get the feeling he's evading your concerns and questions, you know it's time for a little self-preservation. Figure out where you want to be - I'd hate for you to be hurt, neglected, or abused in any way.
From what I've read of the thread, you are the more mature and adult of the two of you - but of course you are, you're the female. All us guys are at least 1/2 little boy, mentally undressing our English teacher, the check-out girl in the supermarket, and the boss's secretary. That's normal. But, as my wife says, it's okay to look at the menu, as long as you don't order anything.
That you have concerns and don't feel free to address them withouth it sounding like an accusation is a cause for concern it itself.