Those people are saying that this has been the case since the start of lockdown are technically correct, but as is often the case you're missing the subtlety, which is the inconsistency, and the bigger picture, which is the broad contempt the inconsistency betrays for ordinary people.
Yes obviously its impossible to have sex while social distancing and if you weren't allowed outside the household and your partner lived outside the household that meant no sex.
I think that is upsetting to those of us in non-cohabiting LTRs is that while the law is slowly easing around things like shopping, exercise, having gatherings in the garden etc, it seems to be actively hardening up against people committing the very mundane sin of being in a relationship with someone you don't live with.
I'm sure its not by design, but it seems so punitive that people who don't cohabit are being subjected to something so tough when things are really easing up across the spectrum.
And its also playing into a nasty, 1950s seam that runs across society (and through mumsnet), which states that if you don't cohabit you can't be a legitimate couple, just a pair of lonely desperate people looking for sex wherever you can get it.
For people like me who have serious and loving relationships but who can't cohabit for a variety of well thought-out and private reasons, its insult to injury. And although almost certainly not deliberate, its just another example of how this government has absolutely no concept of how this is affecting ordinary people who don't have neat lives with non-working spouses, 2.5 children, nannies and housekeepers etc.