Why can you not bond 2 metals together, but you can bond 2 non-metals together and you can bond a metal with a non-metal?

The answer to this question would be: because the low ionization energy or the energy needed to remove an electron.

So it is easier to send the electron out than taking it. If the atom both metal, they both more likely to send electron but no one takes it so it is hard to make it a stable bond. That is why metal-metal covalent bond is hard to achieve