How absurd. There are a multitude of reasons your partner could be of the same race, most of them not being remotely related to race.

Not necessarily, by any means, though it can certainly be a factor.

Most romantic relationships begin with initial physical attraction, at least in part. It's generally rare for someone to seek a romantic relationship with someone they have no attraction to whatsoever. Some simply aren't attracted to other races, naturally. Initial attraction being preferential to one race or another is not racism; I don't believe physical attraction is something that is consciously chosen, as such it can't be said to be prejudiced in any meaningful way.

And if one is attracted and open to all races more or less equally, if the person they end up marrying happens to be of the same race, that's just the way life panned out, and it's not really any different than if they had married any other race.

That said- racism can and does play a part in mate selection; racism can override that which we are attracted to naturally. That KKK leader who was found with a black prostitute comes to mind, after all- obviously there was attraction, but his twisted views prevented the possibility of ever marrying a black person. That doesn't imply that all or even the majority of cases of racially homogenous marriage are based in racism, however.

For that matter, someone being married to a different race does not imply they are not racist, either. For example, a white person may marry a native american person and still hate black people, or vice versa. I'm fairly sure there are even cases of marriages between a dominant partner and a submissive partner that the dominant one is racist towards, all being incorporated into some kind of BDSM lifestyle (by which I mean I've heard of such things from sources I generally hold to be credible, but not ones that I could expect others to hold credible on my word, and cannot confirm such relationships personally.)

No more or less racist than being married to someone of a different race.

Only if their race was a pre-requisite of "marriage materiel" to you.