I quit using my invisalign over a year ago. Can I continue, and if not, what should I do?

As the majority of your attachments are placed on surfaces of your teeth, where they are accessible to the normal cleansing action of your lips, cheeks, and tongue, this is not too likely. That being said, it is still advisable to clean your teeth after each and every meal.

Unfortunately, your photos do not show enough of your mouth to properly diagnose your case. However, if you do want to straighten your teeth, Invisalign is definitely your appliance of choice

When your Invisalign was completed all of your teeth should have been hitting simultaneously. If as you say, one tooth is hitting the other that shows me that your Invisalign treatment was incomplete and that you should return to your Orthodontist for a refinement.