At that age they don't understand object permanence, meaning "Mommy and Daddy disappeared!" You can play games like put a toy under a blanket "Where's the bunny rabbit?" Then pull the blanket up "There it is!" keep doing this until he figures out he can look under the blanket, and then put the blanket over your head "Where's mommy?"
When you leave the room, talk to him or sing to him so he knows where you are. I have things all over the house to put my baby in- a playsaucer in the living room, a Johnny jump up in the laundry room, a bouncy seat in the bathroom and of course a highchair in the kitchen. I just move her around with me. I also have a sling I carry her in. Now that my daughter is 12 months she understands that I am coming back but when she was younger she spent a lot of time where I was. And that's ok!!
When they get to be about 1 they start learning some independence but when they near 15 months is when they start getting attached to things. So that means that 1 is the best age to wean from the bottle, pacifier, being carried all the time, ect. Anything you don't want them to carry with them at 2, 3, 4 years old. But if you wait until 18 months it's extremely difficult to wean them from things!
But at this age, if you want to keep him with you all the time that is perfectly acceptable!!!
S., mom to four girls ages 12 months, 3, 4, 5.