I think that the quality of relationships depends less on the fluid intelligence of the partners, or on anything else they might have in common, and more on their level of emotional maturity (empathy, non-self-absorption, communication skills, generosity), as well as their attachment to and affection for one another.

You may become more attached to, or feel more affection for, someone you believe to be intelligent, but then again you might achieve the same emotional connection through, for example, shared life experiences. Intelligence and common interests may make a mate more entertaining, but in my experience it's really not terribly important for my boyfriend to entertain me; we can always go see a movie or play a game together for entertainment.

I'm arguing, in short, that intelligence is mostly irrelevant to relationship quality.

On a more personal note, I can testify that, however much you might admire intelligence per se, it is a terrible idea to date someone who is nearly but not quite as intelligent as yourself, who is also crushingly insecure.