I believe what Blondiemonster believes, as many people and cultures do, the spirits of our lost loved ones visit us in our dreams. Oliver misses you too and he wanted to comfort you and let you know he is well and happy.
When my husband was young, he lost a beloved springer spaniel and the family was devastated as they loved her so much. But, they believed she came to visit them frequently when they would feel a brush against their legs under the table (where she used to lay) and there were even sightings of her dashing through the kitchen door.
If you are fond of reading, there are some really good books about pets and the afterlife, a good one I read recently is "Angel Dogs" and there's another one, "Cold Noses at the Pearly Gates".
Cherish his memory and cherish that dream, I'm sure he'll come back for a visit when you least expect it. It's been only a few months and it will take a long time for you to heal. I think Oliver is helping you to do that. Take care of yourself
Desrae, guardian of two tri-coloured cavaliers, Belle 3 years old and Bobby 1 year/8 months.