We've hit it off ever since we knew each other.我们从刚认识就很投缘。

俚语表达hit it off with sb.，意思是“to be friendly with each other immediately”（与某人很快就能合得来）。
　　例句：
　　She hit it off with Dean and soon the two of them set out on a cross-country adventure.
　　她和迪恩成了好朋友，不久，他俩人就一起去跨国旅行了。