What should i do about my sons autism?

my son has minor autism and is in preschool hes made progress but lives with my grandparents i fear that he has abandonment issues since i ama single father and in the army...i have the oppurtunity to have him with me but i want whats best for him...i feel leaving him with my grandparents and not changing his routine is the best decision for him...but ive mssed out on so much and want to be with him and help him grow...but i dont want to hinder any growth or progress he has already achieved i dont wanna have him take 1 step forward that cost him 8 steps back...i love my son and i dont want him to feel differently about me....i also feel bad because this is a heavy burden on my grandparents can anyone give me advice?