I find it interesting that you use the phrase "supposed to" in your post title. I usual pause and reflect when I hear myself saying "supposed to" or "should" because it usually means I am comparing myself to somebody else's standards.
If your current level of contact or "missing people" is working ok for you, then it doesn't matter. If it isn't, then I am sure there are plenty of strategies you could use to remind yourself, for example like putting a reminder in your calendar.
I also have an "out of sight, out of mind" approach to people (full disclosure, I'm not autistic) but I have found ways to stay connected with others. For example I scroll through my whatsapp contacts to check if there is anyone I want to contact who I haven't spoken to in a while. I also have routines to remind me to call people, for example, when I have a really boring chore to do I call my Dad. He keeps me company while I accomplish the task so that it is less boring and he is happy that I called him. A win-win!
Hope you find this message helpful but like I said, don't be too hard on yourself, comparing to "supposed to"s and "shoulds". 