Subject + 在一起
在一起 (zài yìqǐ) means "together" or "to be together" and describes people or things being in the same place or in a relationship. It can function as a verb phrase meaning "to be in a relationship" or as an adverbial expression meaning "in each other's company." It is one of the most common ways to express togetherness in Chinese.
我们在一起三年了,感情很好。
Wǒmen zài yīqǐ sān nián le, gǎnqíng hěn hǎo.
We've been together for three years and our relationship is great.
朋友们在一起聊天总是很开心。
Péngyǒumen zài yīqǐ liáotiān zǒng shì hěn kāixīn.
Friends chatting together is always a lot of fun.
周末全家人在一起吃了一顿火锅。
Zhōumò quánjiā rén zài yīqǐ chīle yī dùn huǒguō.
On the weekend, the whole family got together and had hot pot.