If my wife felt that way a condition on marrying her would be that she never, ever speaks badly about BYU, rubs anything in my face, or cheers for the Utes in my presence.
My in laws are also Utah grads and fans, but my wife is a BYU fan and doesn't care about Utah at all. Her parents and family rarely ever bring up sports because they know how much I love BYU. The conversation would not end well so they avoid discussing it.