The antonyms for the phrase "all by oneself" are many and varied, depending on the context in which it is used. A few common antonyms include accompanied, surrounded, supported, assisted, and helped. Accompanied means to be in the company of someone else, while surrounded means to be enclosed or enclosed by others. Supported and assisted both suggest help from others, and helped means to be given aid by somebody else. In general, the opposite of being alone is to be with others, so many antonyms for "all by oneself" will involve some kind of social interaction or relational dependence on others.