we've told the sitter "dinner with friends" for 18 months and i think shes onto us

context. F35 dh 37, kid 9, sitter is a lovely 50something neighbour, weve used her almost every saturday for nearly 2 yrs. our go-to line forever has been "we're having dinner with friends" and that worked GREAT initially bc its boring, its specific, its socially expected for ppl our age. problem is. weve been having "dinner with friends" every single saturday for 18 months without ever once mentioning the names of these friends, without ever inviting them to our house, without our sitter ever seeing any of these supposed friends. she def knows by name everyone weve had over for an actual family bbq and they do not match the "dinner with friends" calendar at all. couple weekends ago she said, very kindly, "you must have such a fun friend group, i never see them around tho". i made some bs about "oh theyre across town, we always go to theirs bc they have a bigger place" and she nodded but i could tell she was being polite. it was the same nod my own mum does when i say im fine. i feel like our cover story has a structural flaw which is, real friend groups have names and faces and the sitter eventually clocks that ours is mysteriously faceless. do other ppl give their cover friends actual identities?? do i need to start dropping a fake name into rotation like "we're seeing tom and rach tonight"?? does that not just dig the hole deeper?? or do i pivot to a different cover story entirely. the issue is at this point a sudden pivot would be more suspicious than just continuing the slightly cracking version we have now.