tugovati

1. to grieve; to mourn
   Cela porodica još tuguje za bakom. — The whole family is still grieving for grandma.
   Nemoj da tuguješ zbog njega, nije vredan toga. — Don't be sad over him, he isn't worth it.

For a person: tugovati za + instr. (za nekim); for a reason: zbog + gen.