Will I have to come get acupuncture forever to keep feeling good?

Likely not, but this also depends on the reason(s) you're getting treated in the first place.

For short-term issues, a handful of acupuncture treatments should do the job. For chronic or long-standing issues, a maintenance schedule of some sort would be in order to keep systems running smoothly and steadily after the initial period of relief and change.
 
For example, patient Melissa comes in for help with pain and swelling from a new ankle sprain less than 24 hours old. This type of injury responds best with acupuncture treatments two out of three days, which would probably be plenty to help Melissa's body sort out her injury completely.
 
On the other hand, David gets acupuncture treatments to work toward better management of long-term anxiety and insomnia that he's struggled with for five years. Chances are good he'll start to see clear changes in the pattern and intensity of his symptoms with steady treatments over four weeks or so. After this time, his acupuncturist will likely recommend regular but less frequent treatments for another stretch of time to help make sure the process of change continues moving forward. Once David finds himself in a place where he's consistently happy with his sleep and anxiety levels, we'll know it's time to dial back the frequency of his treatments even further. The aim here is to provide as few acupuncture treatments as possible while maintaining gains made.