I think of every standalone fic as a new circumstance. In fiction, and even in RL, sometimes people are drawn to a partner because of the similarities between them. Sometimes because of novelty or complementarity they're looking for someone completely *different.* Even a cliched fictional character has at least a few attributes, and a well-written one has many attributes.

So, Fraser is someone who puts the highest possible value on loyalty, and he and both Rays immediately form relationships of loyalty and trust. (Also, RayV talks to his dead father, which not everybody does.) Lots of people I know think that CKR is really hot, so why shouldn't Fraser feel that way too? OTOH Fraser is someone almost completely devoid of conventional career ambition--maybe he'd think Thatcher was fascinating because she *is* ambitious. Maybe he'd bond with Turnbull because of a mutual love for chilly rural towns.