"The reason I can't tell him the truth is because I used to promise things in the past and never stick to them. For example, new diets, exercising.
Ha,I don't know how many times I told everyone "BUT SERIOUSLY THIS TIME IT'S DIFFERENT,THIS IS IT!"
So just tell him that you are not drinking right now since you are on a health kick (isn't that your name you go by?) and that is the end of conversation.I bet he won't want to get into it more...
I actually have quit drinking in the past to lose weight with all the empty calories in drinking.