Fleas do not just live on your dog, they live in the environment. So as well as putting your dog on a monthly flea preventative, you also need to treat your house and yard.

Also keep in mind, even after the fleas "go away", you should still keep him on a monthly flea preventative because... well, the best comparison I heard was this:

A group of vet students went to visit a patient about a flea infestation on a dog. The owner was a dentist. They had seen the dog a few months prior for fleas, suggested some products and sent the dog on his way. When they saw him the second time, the dog was absolutely covered in fleas. They were amazed and asked the guy why? The dentist said "Well, when I had him on it, the fleas went away, so I stopped using it." They were taken aback, and said "If it worked so well, why STOP using it?" and then made the comparison -- it's like a long-time patient who's always had perfect teeth coming in to see the dentist. His next visit he comes in and his teeth are covered in cavities. When asked why, the patient says "Well doc, brushing my teeth worked so well and I didn't have a single cavity, so I stopped!"

I paraphrased that, it isn't word-for-word, and the name of the man who told it completely escapes me now, but I think it's a really good reason why dogs should always stay on a monthly preventative year-round. Just because the infestation goes away on the dog does not mean he won't ever get them again, especially if they're in the environment

Capstar kills them quick, but you will still have to take care of the fleas in your house in yard. I would ask your vet about what is safe to use on the environment, but in addition I would keep him on Advantix or Advantage (or whichever flea preventative you prefer). Also keep in mind that you may still see a flea or two on your dog while he is on the preventative from time-to-time, but rest assured the product IS working. Most prevent the fleas from biting, so eventhough you may see a flea on your dog, it doesn't mean it's being bit

Another piece of advice is try not to bathe him too often; once a month should be fine, but any more can dry out and irritate his skin.

Good luck!