I'm going to be distant to my fiance who's ex just passed away
In what way are you going to be distant?
We used to text each other every day but now I am going to stop doing that.
Your partner may be grieving his ex, but that does not change how he feels about you. You should be there for him at this difficult time, instead of making him feel alone. If you do not provide support, he may feel the need to reach out to someone else who will.
That's fine. I don't want to continue talking to him every day.
Well that is your decision. Just know that someone dying is a very sad thing. Your partner grieving about their ex has nothing to do with their feelings with you.