if you´re any serious about photography you wont get around getting a flash / several flashes sooner or later. you have so many additional possibilities with a flash, especially if you use it off-camera with a remote trigger.

That's would probably be the best use for a flash, but I think I still have a long way to go before I can master that.

I think I should borrow one and see if I really need it.

Knowing you photos, you would have more use for a macro lens.

If you are not willing to make money with photos I suggest to buy the flash later as you won't need it that much.