Nowhere in Fremantle's account does he state that Longstreet was drunk. He was not with Longstreet during the assault of July 3, 1863, joining him after it was repulsed. Longstreet had already arranged a defensive position in anticipation of a US counterattack. This being done, according to Fremantle:
He asked for something to drink: I gave him some rum out of my silver flask, which I begged he would keep in remembrance of the occasion; He smiled, and, to my great satisfaction, accepted the memorial. He then went off to give some orders to McLaw's division.
<Arthur Lyon Fremantle,
Three Months in the Southern States: April, June, 1863. (Edinburgh: William Blackwood and Sons, 1863), p. 267.>
This is certainly evidence that after the assault Longstreet took a drink of rum. It is not evidence that "Longstreet drank alcohol during the Charge and gave orders under the influence" as Fremantle wasn't with Longstreet at that time.