Next time you see him tell him to stop mucking about with your chromebook and if he ever touches it again, you're going straight to a teacher to report him.
Stop falling into his frame where he thinks it's OK to take your valuable property and chase after him for it.
Assert your frame that you're a high value person with a right to maintain possession of your property.
Even if he loves you from the bottom of his heart, he needs to shape up his behaviour, big time, to be worthy of your attention.