My recent ex girlfriend would take certain things we were about to do together (traveling, going to the spa, going to a particular restaurant close to my house, spending the day at a museum, etc.) and would just automatically assume that I had already done that same thing with some unspoken past ex of mine, and get preemptively sad, upset, and self-conscious that she wasn't "the first"... What? Life isn't all about firsts, why even get upset about that? So what if I've already done something before with someone else, I am still going to enjoy it with YOU right NOW. Maybe a lot of people do compare past experiences to current ones, but I don't find that very fulfilling, so I just don't. It's a lot easier to just live day to day.