this is what i would say " (insert friend's name here) you are a very important person to me, you saved my life and that really means a lot to me & you are the best friend a person could ever ask for i don't want to lose you as a friend because you mean so much to me and i am so grateful for what you have done for me..but it seems like you are avoiding me a bit and i'm really scared that you don't want to be my friend anymore, i hope i'm just overreacting but i just had to ask because it's really been bothering me..."

hope this helps!