SHERRY: Yeah, I’ve been wanting to tell you, actually. Chris and I had a rocky stretch. I thought for sure he was out the door. I mean, he was so distant and hardly ever talked. I wasn’t even sure if I was gonna tell him about the baby. I thought I was gonna either go it alone, or not go through with it at all. I mean, I was kind of in the same position that you were in when you were pregnant, do you know what I mean? … I decided that I would tell him before I made any decisions, and that was the weekend he was with you and Rory, remember? There was a wedding or something . . . Well, I don’t know what happened or what you said, but whatever it was, it worked. He came back a changed man. All of a sudden, he was so attentive and devoted, and so willing to make it work. He said that he’d missed out before, and he didn’t want to miss it again. And I just credit a good portion of that to you.
Christopher said that he and Sherry had problems in their relationship, but from Sherry’s perspective, it was that Christopher was withdrawing from her and “quiet quitting” their relationship.
It doesn’t really make sense that Sherry credits Lorelai for changing Christopher’s attitude. Sherry decided to tell him about the baby, and Christopher returned to Boston, saying he was there for her and the baby, and didn’t want to miss out on fatherhood for a second time. Why would she think that Lorelai made the difference, rather than the knowledge he was going to be a father?
My hunch is that Sherry intuitively knew or suspected that Christopher and Lorelai shared something on their weekend together (if your boyfriend you’ve been having problems with spends a weekend with his ex, there’s a good chance you’re going to get suspicious about it).
I think she tells Lorelai that it’s because of her that Christopher returned to her as a way of warning Lorelai away from Christopher, or to let her know that she knows she and Christopher slept together, and that they don’t need to discuss it any further.