Over here, they recommend that you BF exclusively for 6 months, and continue until at least 12 months. I personally did not continue that long, but not really by choice. With my first, I ran out of milk at 4 months, after having pneumonia pretty badly, and with my second, once I gave her a bottle of EBM at 8 months, she didn't want to nurse anymore. (she much preferred being able to eat and see the world at the same time.) I pumped for a little while, but things got too busy for us, and after about a month, she went to formula.
My sister's baby weaned herself cold turkey at 7 months. (was she ever in pain after that!:eek: ) So sometimes, they decide for themselves, and sometimes circumstances make nursing too difficult. I'd say give your baby the best start that you can (as you have) and keep it up for as long as BOTH of you are happy, and try not to have any guilt about the outcome one way or the other!
All the best!