Btw I believe in owning l lenses only
I knew a guy who believed in driving only Mercedes cars. He had to give up his apartment to afford the payments, and found living inside a C-class to be very cramped.
Personally, I own mostly L lenses. But then, I'm not a student anymore...
I don't think you get it
selling gear is the only way for me to own L glass
I suppose it comes down to philosophy...but in all honesty, with an L-lens you are paying a significant premium for what amounts to a small boost in IQ and/or build, and in some cases, not even an IQ boost - the 17-55mm and 15-85mm EF-S lenses outperform all of the UWA and 'general purpose' L zooms (24-70, 24-105, 17-40, 16-35 II, with the possible exception of the 24-70 II) when compared on the same APS-C body.
The most important consideration in choosing a lens, IMO, is focal length. You pick that first, then make the other decisions. Having only a 100mm lens for an APS-C camera is going to be extremely limiting.
If I were going to have just one lens for an APS-C camera, it would be the EF-S 17-55mm f/2.8 IS. I could certainly see selling your 18-135mm to help fund that lens. Later, add a used extension tube and you've got near-macro capabilities.