Why would my boyfriend do this?

My boyfriend and I have been dating for 8 months. In the beginning of our relationship I snooped around his apartment (I know this is wrong) and came across a box he had with memorobelia from his ex girlfriend (cards, letters, little trinkets, etc.). Well, for V-day and several other holidays I've given my boyfriend cards or letters. He has kept them for a little while, but then he throws them away. I would never throw away something he gave me and I'm not sure why he would throw away the stuff I gave him, but yet keep the things his ex girlfriend from 3 years ago gave him. He even moved across the country and took this stuff with him. But mine gets dumped in the trash! I asked him why he threw it out and he didnt have much of an answer. I got really upset and said "so you dont keep things from your ex girlfriends like this" and he outright lied and said no. I couldn't call him out because then he would know I snooped. Is this something I should be upset about? What does it mean?