A filling for a small cavity keeps falling out. this is the 5th time i will have to get it fixed in 1 1/2 years. should i find a new dentist?

Filling falls out: If you have had the same tooth restored with the same small filling five times in a year and a half, it would seem there is something drastically wrong with the execution of the restoration. Small restorations should last a very long time owing to the strength and mass of natural tooth structure surrounding the restoration. I would check out another dentist.

Different material: White fillings (composite resin) are chemically bonded to teeth, so rare for them to fall out. They are very moisture-sensitive. If the tooth gets wet while placing it, the bond will be much weaker. Fillings placed where the gums have receded are under a lot of stress & can sometimes come out. If this is the case, a glass ionomer filling may work better. A night guard can help if grinding teeth.

Depends: Depends on where the cavity is. If it was on the edge of a front tooth/incisor, those can have a tendency to chip off if you are not careful about biting into hard food. If its in the back of your mouth, with the bonding process being very technique sensitive, if any saliva hits the tooth in the middle of bonding, that can compromise the bond and make it more likely to fall out.

Frustration: I understand your frustration. You may need another type of restoration- crown, etc. To keep going back is counterproductive and frustrating. I would possibly consider a second opinion.

Einstein : Einstein defined insanity as doing the same thing over and over and expecting a different result. Probably time to move on.