as a rule you shouldnt mix american and african cichlids, but i ahve to admit ive done it in the past, and it's worked fine.
some people have absolutely crazy tank stockings and it still works! its down to luck, care, water quality, and how the tank is set out, with the africans they require alot of individual caves etc for territory!
i don't think its right to tell you you did wrong, cause 2 months shows the tank is obviously stable for the time being and i would be thrilled if my gf got me a GT like that =P
hope all goes well =)