GDB already has a TUI.. it's pretty "vintage" though. I looked at the screenshot at the top of the repo README and it looks like it has a lot more creature comforts (read: any at all compared to GDB).
Fun fact: gdb tui was the last straw that made me start working on nnd. I tried it for the first time, and it was taking 2 seconds to respond to every input, and that made me so angry I started researching how to make a debugger :)
I had pretty much the exact same experience with my debugger (uscope). Your debugger looks awesome, nice work! Hopefully I'll have time to get back to mine at some point (or hopefully RAD comes to Linux first haha)
check out [cgdb](https://github.com/cgdb/cgdb) - ncurses based gdb tui, with vim bindings. It's no longer actively worked on, but is decently maintained with bugfixes etc AFAIK.