I don't have diastolic dysfunction, but read a little bit about it here: https://my.clevelandclinic.org/health/diseases/23434-diastolic-dysfunction

It sounds like some of the causes are treatable. Did your cardiologist discuss possible causes with you? It also sounds like there are some negative effects of leaving it untreated. But I am not a medical professional.

If what you describe is the entirety of what was discussed with your cardiologist, I'd consider getting a second opinion or at least discussing it with your PCP.