I fall squarely into the case of multiple things being true for me with this.
1. My wife and her family are all Ole Miss people who for 20+ years have been incredibly kind and supportive of me and my obvious and demonstrated fandom for Mississippi State, being incredibly gracious to me and any of my people who have traveled to Oxford with tailgates and anything else, and are genuinely happy for me when MSU does something good. On that account I am always very happy for them when their team accomplishes something good and I am usually even able to want it to happen for them. We do not trash talk each other and are pretty objective in analysis of the other's side (except for my 8-year-old nephew who once made amends by mailing me a hand-drawn and colored M-State logo in apology for some Egg Bowl trash talking).
2. I fully recognize what a complete and absolute insufferable nightmare it would have been for Ole Miss to win a national championship amongst the majority of that fanbase, and I am not at all sorry that I don't have to deal with that.
These two things exist simultaneously within me, and I think that's fine.