Science

i, uh, hm. well, in a marriage, you don't know if someone is exploiting your goodwill, but ideally you marry someone who you don't have to actively worry about it e.g. someone you can trust

relationships aren't a hard science, but that doesn't mean there isn't science about them. for example, you could check out the book, "a general theory of love". or you could check out the work of john gottman on relationships and love, he's done a ton of work on them

for more general information on like, how humans work, you can check out paul ekman's work on facial expressions and the facial action coding system (FACS). i'd also recommend marshall rosenberg's non-violent communication - i don't recall how strictly research-based the work is, but he (until he died, anyways) and his org do trainings across the world in this stuff, and he has a phd in clinical psychology, so i... think... it has a reasonable foundation? (it's been a while since i read it)

and of course, because trauma invariably deeply affects relationships, you can read "the body keeps the score", which is maybe the foremost research based text for the layperson about it

sorry, i'm not sure how open you are to actually receiving this kind of information... it's totally understandable if you're not. i used to feel a lot like you, i think, kind of unsure and untrusting of others. and all of these things are things i've read and learned from that have given me a lot more confidence about interacting with other people in general

obviously, the knowledge itself isn't enough, but maybe you'll find it helpful nonetheless