No, I don’t think it’s related as the extremes thing predates the relationship thing. I have for quite some time experienced or sought out relatively high highs and low lows, and also get very very passionate about something. Used to be radio and music. Still love music. But now it’s mountains. Those passions have always been my compass in life.
My brother follows a similar trend. If he's into it, he is into it. Currently it's hiking and long distance running. He has hemophilia, so this is quite the feat on it's own. Honestly didn't expect him to gravitate towards movement being his focus, but I guess after years of restricting himself he's found he loves it.
Hah! I am also a distance runner (trails, 50km), and am extremely anemic (working on this with my doc) so can very much relate to your brother in those regards.