They were completely absorbed in each other. [+ in/by]

两人彼此倾心。

He had discovered politics and was rapidly becoming absorbed by it.

他接触到了政治并且迅速地对它着了迷。

I get so absorbed in doing something that I am unaware of things happening round me.

我做事太过专心以致于对周围发生的事情丝毫未察觉。