Patch tube, Yes/No?

So in the past few months i've had 3 slow leaks. Each time I put the old tube in a bucket of water to find the hole, check the tire and then install a new tube. So far all 3 are tiny holes most likely caused by a thorn.

Since I mostly ride solo and can get 30-40 miles from home at times, I've opted to always use a new tube. But at $10 per it's starting to get expensive.

I once went 18 months without a flat and am concerned of a patch failing over time.