I'm new here so I apologize if this was put in the wrong category. This is about the behavior of my male so I thought behavior was the right place to go.

My sister and myself have gotten two sugar gliders (male and female) on St. Patty's Day 2016. My male, Gizmo, is an absolute sweetheart and my sisters female, Clover, is nippy and shy. They have both been together their entire lives and have reproduced once according to their previous owners.
Just later last year I think it was, Gizmo started having behavioral issues towards Clover. They've been perfectly fine living in harmony together before then. All the sudden Gizmo has gotten food aggressive towards Clover and crabs at her and will even tackle her if she gets near the food (they have two bowls but fatty Gizmo will guard one until he finished eating and then go to the other). Now, just tonight, Gizmo was showing aggression towards Clover with the water.
They are not starved, are fed BML diet every night, and always have water. They sleep together perfectly fine with no problems, it's when it's dinner time he gets aggressive towards her (but perfectly fine with me and my sister around the food).
I have no idea how this started or why. Does my glider have a medical problem? Should I have him see a vet? I'm not worried about Clovers eating at all (she isn't thin and looks healthy) I'm just worried if he's gonna hurt her when he tackles her or if it'll get worse.

Thanks in advance.

It's difficult to find out why food agression starts, and there is no real solution other than putting more feeding stations in order for both to eat without being in direct view of the other.

If there is no other agression outside of food, it is possibly just food agression, however, sudden change of behavior toward a member of the colony can be a sign of illness, gliers tends to push away individual that they feel present a danger for the colony, so in case of doubt, a wellness check by a vet for both gliders can be a good idea.