Can I continue getting facial fillers forever as this is what I want?

Great question.  You can absolutely use fillers long term.  Whether you're using hyaluronic acid fillers or a combination of HA and permanent fillers, I would caution against relying solely on them.  We tend to forget that we can stimulate our own collagen and elastin with the right technologies.  It's usually a combination of procedures (fillers, laser, radiofrequency, neuromodulators) that keep us looking youthful but, more importantly, natural.  I hope this helps! Dr. Dima

There should be no harm in continuing facial fillers for an indefinite time.  The fillers that are FDA-approved are safe over the long term.  

Currently, there is no evidence that there is a problem with repeating fillers.   Generally, think of fillers as short term: 6-12 months Juviderm and Restylane, longer term: Radiesse, Sculptra (2-3 years), and long term / semi permanent Bellafill.  
Restylane and Juviderm are hyaluronic acid and these get digested by the body over time and the affect dissipates away over time. Most are FDA approved to last 6 months.  Numerous variants on hyaluronic acid fillers are available with slightly different features based on cross linking and size of molecular size of individual particles.
Radiesse is a biostimulant that promotes collagen but breaks down over time (2-3 years)
Sculptra is a bulk filler biostimulant as well very similar to material in some absorbable suture.(2-3 years)
Bellafill is a biostimulant using polymethyl methacrylate (PMMA) beads.  These stimulate collagen but do not get broken down my the body.  This is why this is considered a semi-permanent filler. (FDA > 5 years)  Bellafill is the only filler approved for acne scars with 5 year follow up data to support effect.
Nearly all fillers are FDA approved for nasolabial folds but many off-label uses are commonly performed. One key to remember is that the biostimulant fillers are making collagen which is thicker/less pliable which makes the hyaluronic fillers better for less dense tissue tissue such as the pink are of the lips.   
As of now, no biostimulant filler should be used on the pink part of the lip/vermillion. Biostimulant fillers also do not have a reversal agent such as hyaluronidase used on Restylane or Juviderm. Steroid injections can non-specifically reduce biostimulant fillers.   The hope would be that reversal agents are not necessary as this defeats the filler placement.