I used to have a 2007 Breva 750 and had the same problem. I posted the problem on this forum and someone gave me the part number of a better replacement spring (aftermarket brand). I replaced one of the springs with the new one and never had another problem. I no longer have the bike or the number but maybe someone with the number will see this and pass it along. For the time being, you should use a nylon tie and strap it to the frame so it will stop falling until you get it replaced (that is, if you have a center stand?)
It's Moose Racing exhaust spring M7712 at 3.3 in (83mm)
Lubrication is the easiest remedy. Use a spray, and just keep up with it once is a while.
Other options:
The sidestand nut might be loose. Remove the left muffler to reach the nut,
and tighten w Loctite.
Put a copper collar on the pivot, which lessens friction and gives good
operation. It's Jim Long's idea. Found at Lowe's, labelled as "Repair Coupling
Copper" 1/2 inch internal dia.
Bend the factory spring to get more pull. Take the factory spring and bend a new hook in the end. This shortens it and adds tension. Do this by taking it off, heating the end with a torch, and bending. Don’t let the coils heat up, as this removes their temper.