The word forever is too strong to be used in that sense.
Bitcoin price will always change, sometimes it will be up and sometimed down so in that sense it will always increase.
But generaly speaking I think that market will define some upper price that will the bigest that Bitcoin can achieve and it will not increase above it.
This might be 20.000$, 200.000$ or 2 millions $, we can't know that figure.
This word is not strong, as you said, but bitcoin price will be getting more expensive with the time goes by. The reason behind this is all about the supply. The supply is very limited and mining bitcoin is getting harder and harder every 4 years.