I guess I'd better get going. 

我想我得走了。

I'd=I had

had better

不得不

I'm getting drowsy, I think it's time for me to go now. 

我有点儿困了，我想我该走了。

I hate to leave, but I have an early day tomorrow. 

我不想走，但是明天我得早起。

I suppose we had better hit the road. 

我想我们该出发了。

I'm going to take off now. 

我现在出发了。

I have to go now, I'm in a rush. 

我有点儿急事，我得走了。

I'm afraid we have to leave now.

恐怕我们得走了。

Oh my god, I didn't realize what time it was. 

天哪，我都没注意已经几点了。

Dialogue1:

A: Oh, look at the time. I must be getting going.

天哪，看看都几点了，我得走了。

B: Is it that late already?

已经这么晚了吗？

Dialogue2:

A: Do you have to leave so soon?

你真的这么着急走吗？

B: I would love to stay, but I really have to get back. 

我也想再呆一会，但是我必须回去了。

Dialogue3:

A: I really enjoyed visiting, thanks for having us.

我们这次来访很开心。谢谢你邀请我们。

B: It's been a pleasure. 

我得荣幸。

A: Well, I think I'd better get going. 

我想我得走了。

B: Do you have to leave so soon?

这么着急走啊？

A: I promised my son to go fishing tomorrow. So I have to get up early. 

我答应我儿子明天一起去钓鱼，所以我得早起。

B: Oh, well. Thanks for coming over and bringing the nice wine. 

好吧，谢谢你今天能来，还带来了这么棒的酒。

A: No problem. I think your place is fantastic and the meal was great.

没什么的，我觉得你家真是太棒了，晚饭也做的很棒。