to leave a wife, husband, or partner in order to have a sexual or romantic relationship with someone else

Did you know that Hugh had gone off with his sister-in-law? 你知不知道休跟他的嫂子好上了？

to take something without getting permission from the owner first

I wish you'd stop going off with my car without asking me beforehand. 你连个招呼都不打就开走我的车，我真希望你不要再这样了。