We can't really say "forever" because people think that bitcoin is the last improvement we have on money. Fortunately for the future people (no idea if we will see it) the technological improvements are going on every single day, literally every single day on earth something better version of something gets created, the humanity reached to a peak point where innovation is either small or big but constant.
So, bitcoin is definitely not the last currency, it will probably continue for decades more but we are reaching to a point where humanity will colonize other planets and at that point do you really think that we will still be using bitcoin? Or dollars for that matter? I think in 100+ years all of the currencies we are using today will be gone and something much better will come to terms.
I also think that there is no such thing as infinite value. It is not only because of the theory presented here, but because possible alternatives could appear and also provide alternative investment opportunities. I think that is the most likely reason why Bitcoin would not increase forever. For as long as there is no such thing as an alternative investment opportunity, who knows maybe bitcoin will indeed increase in value for the time being.
But there could also be a viable different cryptocurrency as well or simply dividend paying stocks which at some point make it more attractive to switch. People will be switching back and forth.