Agree with a few people above that some of the comments here are fucking ridiculous. Whether you think the OP was in the right or in the wrong, why decide to call someone who is clearly upset 'unhinged', 'nutjob', 'you are being a loon' etc etc etc. FFS.
Lets turn the tables a bit. Would everybody be so aggresive if OP had written that she had found these photos and journal, got upset, asked her husband about them and he'd subsequently told her she was being 'fucking ridiculous' and a 'loon' etc? Half of you would probably be telling her to walk out, or at least saying that he definitely had something to hide and there were deeper problems here etc. Instead, she's got upset and come to try and find, a) some support and b) some advice. By and large she's had a barrel-load of abuse.
For what its worth, I think that once you set up home as a family together then actually, you do surrender quite alot of privacy to each other. Esp. regarding things that are left in a box in the hallway with bank statements or whatever. Was OP right to read the journal? Possibly not (though I'd have no issue if my wife read mine - if I kept one - I did agree to share my life with her and that includes my history), but I think it would have been bloody difficult not to after seeing the pics as well (which should absolutely not have been bought into the house imo).
I'm not saying the DH is being a shit, but that he has made an error of judgement either deliberately or by omission, and that it is quite understandable that OP is upset.
Think you just need to have a chat to him somehow. Try not to be judgemental, try not to take it personally. Make sure he fully understands how you're feeling and vice-versa.
Apologies for the angry/judgemental tone above, but haven't really seen comments like this on MN before.