As best I can make out:
Pre-1876: The Belfast & County Down railway approached from the East and terminated at Queen's Quay. The Great Northern Railway (of Ireland) approached from the South and terminated at Great Victoria Street, and the Belfast & Northern Counties railway approached from the north and terminated at York Road.
1876-1885: The Belfast Central railway is built and the GNR(I) ran passenger trains (from 1878) between Adelaide and Queen's Bridge (on the opposite side of the Lagan to Queen's Quay), with a connection to the B&CDR immeidately east of Queen's Quay. There was no connection from GVS to the BCR. A connection to the B&NCR was planned but in the end was built slightly later and made use of the harbour board's lines so wasn't useful for through passenger services.
1885: The BCR closes to passengers but remains usable by excursions and goods.
(1948: Ulster Transport Authority formed, begins closures in 1950s)
1965: A bridge is removed between the former Queen's Bridge and York Road severing the connection to the former B&NCR.
(1968: Northern Ireland Railways formed)
1976: BCR reopened to passenger services, GVS and Queen's Quay closed and services from Bangor and Newry/Portadown/Lisburn diverted to Belfast Central.
1992: York Road closed and replaced by Yorkgate in preparation for rebuilding of cross-harbour link
1994: Link to the former BCR reopened and through services from Belfast Central to Larne and Londonderry/Derry start.
1995: Current GVS reopens due to Belfast Central being not convenient for the city centre.
Nowadays the 4-platform GVS has been outgrown by passenger numbers, and redevelopment gives opportunity for twice as many platforms, longer platforms, a new Enterprise Lounge, integration with bus and Glider transport and better rail capacity at the station throat.
I highly recommend these pages: