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，你先去忙别的吧，以后再聊。谢谢陪我聊天。

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.
我知道我已经占用了你很多时间，而且你肯定还有很多其他事情要做，所以你先走吧，见到你真开心。

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.
与您交谈真是太好了，但是我这次想多多社交并结识一些新朋友，所以我现在应该去了。待会见。

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，我们就聊到这吧。

I need to do the rounds and catch a few people, so I will see you later.
我需要去走动走动并跟其他几个人聊聊，一会见。

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.
我确定Jack对这个话题很感兴趣想要深入聊聊，我来介绍你们认识一下。

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

It was nice to see you, but I've got to run.
很开心见到你，但我得走了。