Help me make small dog and big dog get along?

ive had a pomeranian male for about 1 year ive just r got a female bullmastiff puppy 2 half months old. the pom is very scared of the bullmastiff. when the bullmastiff go to play with the pom they start to fight and the pom bites ect. which fires up the bullmastiff to chase the pom and bite too. how can i make these dog get along? i worried that the bullmastiff will hurt the pom? what can i do anyone plz help. thank you