I don't date, so I will comment on situations which can cause someone to stop talking, and to just sit there.
please stop talking
There can be many reasons for any conversation to lag. Someone may just be considering something the other person said. They may have been distracted for some legitimate reason or are just plain not interested in whatever direction the conversation has taken. Maybe their ears are aching from listening for hours without letup.
Some people may just care to change the direction or topic of the conversation. In any conversation, it's always good to try to talk about something of interest to both parties. After all, conversing is supposed to be a two-way interchange, not a monolog.
I knew a person who would monopolize a conversation literally for hours, until my ears actually ached. I felt as if I were being tortured, akin to a dripping faucet clanging into a metal tub from a leaky roof for hours on end. That tub being fastened securely to the top of my head, and my hands and feet tied so I could not escape. Those hours seemed to to be unending.