Around this time your toddler could start recognizing himself in a mirror - he's starting to come to understand that he exists and is his own person. This self awareness is very rare in the animal kingdom!
Separation anxiety can be severe around now - he realizes you can leave him on his own, but still doesn't yet know that you're going to be coming back. This stems from his very strong bond with you, so it's just a bad symptom of a good thing overall. Instead of sneaking away, for example when leaving him with a relative, make your goodbyes honest and clear, and tell him you'll be coming back from him later.
Start laying down the framework for sharing - it's basically impossible to get them to share now, but start explaining that things belong to other people. "Daddy's shoes, mummy's cushion" etc. This will set the foundations which will come in useful later.
Birthdays of children who are now 18 months old are from Saturday 7 May. 2022 through Monday 6 Jun. 2022.