Why does Snapchat do this

So when someone unadds you on Snapchat their username goes to your recently added. Well my boyfriend was going through my Snapchat, and my ex was in my recently added. It turned into a big argument, & I knew I didn’t add my ex and he didn’t believe me. So I was like hey unadd me, & let’s see if that’s what it is. And sure enough my boyfriend unadded me on snap and he was right at the top of recently added list. F Snapchat.