When is a thing interesting?
I believe that interest level is a term which cannot be constant. It’s attribute is to keep deteriorating. It has to come down. You can never be interested in a particular thing for a long time. You can, if it remains obscure to you forever.
I claim that, this is the same when you consider interacting with people. You can’t always be interseted in a person,look at him or her in awe forever. So to keep relationships alive we need to reinvent ourselves. We need to grow,get better,renew ourselves,so that your counterpart(could be your friend,lover,spouse…) remains attached to you. If you bore them,and if no obligations are in place you ll lose them subsequently.