Will it be possible for me to EVER get another dog?

My labrodoor x ridgeback was attacked by a Mastiff when he was a pup (the Mastiff was also a pup,but much bigger than him,they were playing and things got out of hand) and he nearly had his ear chewed off (he's fine now) he is now 5 years old but he attacks dogs larger than he is out of fear.Last week he bit a German Sheperd and all it did was run up to him.He is the most gentle thing in the world with smaller animals,but dogs of similar size or bigger make him vicious.How do I get him used to big dogs so that I can get a Great Dane? I wont rush into this,I will wait years to get another dog if I have to.