You should elaborate on your scenario a bit more, e. g. name your object and field, explain it's purpose and your process.
As far as I understood, you need to trigger events with different statuses.
First you have to become clear about you data-model: can you have only one active trigger-event at a time or many concurrent to track in parallel with different statuses?
a) case one event
If you have only one, there is declarative point-and-click feature called dependent picklists:
b) case many events
If you have multiple events at the same time to track why you don't create a separate picklist for each trigger event, containing your statuses as values? From the UI standpoint maybe not nice, but should be able to hold all your values.
An other approach could be to create a second object called TriggerEvent__c and put the status there as a custom field Status__c. You would maintain the events in a related list rather than a picklist.
If you have a clear picture in you mind on how the UI should look like and how it should behave I think you'll need to write a visualforce page. But before you do that, you have to be clear about your data-model.
For a better solution you