@DleanJeans Thank you for the answer !
However, I don't know why but this line FlxG.plugins.add(mouseEventManager); doesn't seem to work, so I've change it with FlxMouseEventManager.add(place, onMouseUp); and now it works perfectly !

I'm thinking something like

if(velocity.x > 0 && x >= mouse.x) { velocity.x = 0; x = mouse.x; } if(velocity.y > 0 && y >= mouse.y) { velocity.y = 0; y = mouse.y; }

then something similar for if velocity.x/y < 0, etc. etc.