I know this is an old post but I know the feeling. My bullmastiff had to be put down (probably about 10 years ago now) due to tetanus. He was only about 3. Even now I still shed a tear on occasion especially when I sit and think of those last days and the image of him struggling to eat due to the effects of lockjaw.
We have 3 cats now and they are ours (Clyde was when I still lived with parents) and I'd hate anything to happen to them.
I have wanted another bullmastiff now for about 4 years but I have a 6 year old daughter and am a little scared.