to talk someone's ear off: to talk for too long.
let someone off the hook: to give someone permission to go.
I know I've been talking your ear off, so I'll let you off the hook and catch you later. Thanks for chatting.
我知道我一直在喋喋不休，你先去忙別的吧，以后再聊。謝謝陪我聊天。

I know I've been taking up so much of your time and I'm sure you've got a lot of other things to do, so I'll let you go. But it's been great to see you.
我知道我已經占用了你很多時間，而且你肯定還有很多其他事情要做，所以你先走吧，見到你真開心。

It's been really nice talking to you, but I promised myself that I would mingle at this event and get to know some new people, so I should probably go do that. I'll catch you later.
與您交談真是太好了，但是我這次想多多社交并結識一些新朋友，所以我現在應該去了。待會見。

I see someone I was hoping to catch, sorry, I will have to leave it there.
我看到了想要找的人，抱歉，我們就聊到這吧。

I need to do the rounds and catch a few people, so I will see you later.
我需要去走動走動并跟其他幾個人聊聊，一會見。

pick someone's brain: to learn more about something
I am sure Jack would love to pick your brain about this topic, let me introduce you.
我確定Jack對這個話題很感興趣想要深入聊聊，我來介紹你們認識一下。

It's been nice chatting with you, but I've got to go.
跟你聊天很開心，但我得走了。

It was nice to see you, but I've got to run.
很開心見到你，但我得走了。