Garry's Mod Leak

I don't know if I have the original game and my friend has a leak copy, can my friend and me join to a server?

No gmod leak do not connect to the valve multiplayer servers however single player will be fine, to play multiplayer you would have to buy the copy on steam

Its somewhat can be reached if your friend will host the server, im not sure tho.

if you run a dedicated server in insecure and nosteam you should be able to play together

Nope it wont work, even if it will in some way as a person above said you need to host a dedicated or buy one

I think, Garry's Mod leaks are not good. Please support the devs and pay for it.