Earlier quoted context omitted.
At least few co mingled things, at the minimum mail to same address, joint tax returns, maybe some shared utilities bills, each person using their cards alternatively randomly while being together, some travel (local in city or far), some birthday anniversary stuff photos, few gifts like cards, flowers stuff, time & photos with each other's family, a detailed 4-10 pages of statement about relationship, how they met,…
You cannot do joint tax return when not recognized legally as married in the US, it's one of the benefits. And I'm not sure how marriage to a foreign national works in the US, but it might not grant this benefit. Same address (and checked by immigration official) means you already have a temporary visa. (Same address in another country does not count, easy to fake.) So they already let you in... Having paid some US b…
People adjust (or gain) status all the time while they are here already in US on some other visa. Having a temporary visa is has no good or bad effect on getting green card. Its similar (easy or difficult) in other countries as it is in US, its not "easy" in other country(ies) to fake address if it is not easy in USA.
Pregnancy (removed from all facts, sole pregnancy) is never on its own a proof of bonafide relationship. Who is the bio father? The whole collection of proofs when seen as collective, tells the picture & intent.
USCIS & agencies has to follow a manual & policies & procedure (much of it is published on USCIS's website), & 99% of the time the officer can not intentionally bring a personal bias (exceptions apply). There are millions of cases getting passed, & a single USCIS employee does not decide a single case. Like any other big organisation, everybody is doing apart of process. & they have managers, & managers above them. Even USCIS itself is not above law, people routinely sue USCIS in federal courts to challenge their decisions (or lack of decisions).