Well, Sweetlib, I'm in sort of the same situation.. Anxiety in children is so common.... Only I usually only do it if im nervous my lips are too dry and someone will notice (in which cause it becomes hard for me to stop because the more I lick them, the more I need to in order for them to stay moistened). I do think that it's human nature to lick your lips if you think they're chapped, but in your case I think it's an unhealthy habit you've gradually formed and can easily be stopped by thinking about it while you're out.. Carry some carmex with you.. And then before you are about to lick your lips, remember that your carmex is on, because even if you think your lips are dry, they are not. That's how I usually deal with it.
ive licked my lips for many years. ive stopped since then.
2 things made me stop :
learning that licking your lips only makes them drier (like really dry)
learning that licking lips can result from a self-esteem/image issue. it was for me. always wanting to look perfect.
perhaps its a ''tick'' though, as you say a coping mecanism.
i have tendancy of repeating yes many times a row when im stressed out and i want to say simply one yes =D
i carry nivea essential lip balm everywhere i go now. its the only ''make-up'' i wear lol
its the best lip balm ive ever tried.
regards, take care =).