I was wondering if I'm too heavy for my bike. I'm about 260lbs (118kg). I keep getting flats.
Being too heavy and getting too many flats may be separate issues... On one hand, weight will always seem to increase the rate of flats, as I have discovered by going cross country with 60 pounds strapped to my rear rack.
On the other hand, as long as you are not popping spokes, you are not "too heavy" for your bike.
To phrase this another way, this is not a bike issue, it's a tube-popping issue. If you're getting too many flats, make sure you're running the correct pressures, and maybe get some thorn resistant tires and or tubes.
I ride a Trek FX 7.3 and weigh over 400 pounds. The only time I've gotten a mysterious flat (no nail or glass in the tire) was when I had ridden over 80 miles in about 7 hours. I didn't realize the pressure was going down due to the heat and cooling (random rainstorms) and got a pinch flat.
As long as you keep your tires pumped to the max and you aren't breaking spokes, you should be good to go.
I pump up the tires before every ride to their max. I recommending topping off the air every 50 miles you do - if riding 50+ miles in a single ride.
Also, on a side note, I use to break spokes regularly - until my local bike shop hooked me up with custom wheel build for my bike. Now my bike doesn't even creak on a long hill climb!