You poor bee.
Listen, he's with you because he wants to be, and I'm sure that he is absolutely crazy about you. He probably feels the same about your exes too. Nobody would ever be with someone that they didn't want to be with, and you couldn't be with just anybody because you got hurt in the past.
If he wanted to be with his ex, then he would be - you finding a box of things from his past does not mean that he wants to go back. At the moment, he is completely oblivious to all of this - he is just looking forward to getting home and seeing you, enjoying the present with you, and working towards a future. Please don't let this evening change that for you sweetie, it's really not worth it, You will wake up in the morning and feel so much better - there's a weekend just around the corner for you to enjoy together - life really is too short for you to be hard on yourself like this. Remember, you're fabulous, she's not - and your boyfriend will think that too.
xx