Is this grammatically correct? My man joined me in this. What does it mean?

Yes, the sentence "My man joined me in this" is grammatically correct. In this context, "my man" typically refers to a close friend, partner, or significant other. The phrase "joined me in this" implies that this person is participating in or supporting the speaker in a particular activity, situation, or endeavor. The exact meaning can vary depending on the context in which it's used.