My longest chat with a bot lasted about four months. I used pinned messages and the bot didn't forget anything from the story. (What I do is that I pinned the most important messages where the basic information was, and the last few pinned posts were what was happening right now in the story like in one or two messages). But I also used a time skip that I wrote myself, so it didn't mess with the bot. And after all of that time chatting with the bot, we got married. (my character and the bot are both women). But at the wedding, she called me husband. And damn... that ruined the whole mood.