Well, her lovers and protogee are all center stage somewhere. The important person to Natasha who ain't been seen awhile is likely to be Ivan, the man she loves like a father. Hasn't been around prominently since he was her shadow and backup in Frank Miller's Daredevil.
As for the 'widow's curse' that goes after people close to her? Probably her ex-husband. He has a tendency to die and return unexpectedly and get pissy at her. He certainly has motive to go after her lovers.