Presta Valve Keeps Ripping From Tube
The usual causes for this:


Presta valve in Schraeder hole without proper reinforcing grommet.
Valve crooked, or being forced crooked at the expense of extra stress on the tube/valve joint by riding with pressure too low. 
Burrs around valve hole. Knock down and replace with a neat bevel with swivel deburrer, tapered reamer, small round/needle/rifler file, or sandpaper.
Pump technique allowing the force to get taken in part by this area of the tube/valve instead of bracing the pump against your hand or a solid object. Usually involves a frame pump or mini pump.
Tightening the Presta nut too tight once the tube is inflated. (I.e. reefing down on it. Snugging reasonably firmly is fine, although it does add stress to the material that can only do ill over time.)
Tube too large or small for the tire, causing a stress riser in the valve/tube joint under pressure.


Less common reasons, more in the realm of theoretically possible:


Age. Tubes last more or less indefinitely but they do age out sometime, and the area around the valve is a likely spot since it's less supple and flexible. I've had tubes I've kept going many years without any of the above factors fail this way.
Valve hole a little larger than ideal, causing a lesser version of the "Presta valve in Schraeder hole" problem.
Simple defect.