만나다(man-na-da, mannada)
To meet or get together with someone.
When to use
Planned meeting, Chance meeting, First meeting, Meeting friends
The nuance
Use 만나다 when two or more people come together at a place, whether planned or by chance, indicating a positive or neutral meeting.
헤어지다(he-eo-ji-da, heeojida)
To separate or part from someone.
When to use
Farewell, Temporary separation, Ending romantic relationship, Parting with friends
The nuance
Use 헤어지다 when people separate after meeting, either temporarily or permanently, including breakups or farewells.