I want to tell my friend I am going on a date
Why do you feel the need to tell your friend that you are going on a date?
I think he dated her in the past.
If you think your friend would want to know that you are dating someone he knows, it is good to tell him the truth. Doing so will show him that you respect him and his feelings.
Yes, I figured I shouldn't hide this just in case.
You are a very considerate friend for that.