Of course it's mentally addicting.
Anything that continuously provides happyness, contentment, or social comfort is definately going to be mentally addicting. Some people get into co-dependant relationships with pot, just like they do with alcohol or a person.
Others may find themselves smoking 24/7, and when they try to stop, they can't sleep, they feel like shit, and the total burnout feeling is wayyy too confusing to take control of your willpower.
Just becuase You know you don't need pot to be happy, entertained, or content, doesn't mean others have or ever will realize that.

I used to struggle with it,
but then I gained confidence in myself, in being sober, and in living life,
and now It's no issue.