NPC dialogue script, for loop not working properly?

I have a dialogue script that allows the player to press E on an NPC and start a conversation. Pressing X makes the dialogue progress to the next sentence, and Z exits the conversation.

I have a for loop that's supposed to loop through each sentence that the NPC says, and output each letter, one by one. It's having issues though. For some reason, after exiting the conversation, it tries to output the very first sentence, even though the player has exited the conversation. Another problem I noticed, is that the dialogue lines will be in the wrong order sometimes when you re-initiate the conversation with the NPC.

I'd appreciate any help with the above two problems.

Here's a video of the script in action, and the bugs I mentioned: https://www.youtube.com/watch?v=30WUfX3blEQ

Below is the code portion that is relevant. The for loops start around line 91 and goes to line 119 in the UserInputService function.

--// Services
local RunService = game:GetService("RunService")
local UIS = game:GetService("UserInputService")
local Players = game:GetService("Players")


--// Main Variables
local DetectedNPC = nil
local Detected = false
local Chatting = false
local Next = false
local Exit = false


--// Player
local Player = Players.LocalPlayer
local Camera = game.Workspace.CurrentCamera

local Gui = script.Parent
local Sounds = Gui.Sounds
local PromptLabel = Gui.PromptLabel
local LineLabel = Gui.LineLabel


--// Character
local Character = Player.Character or Player.CharacterAdded:Wait()
local CharHMR = Character:WaitForChild("HumanoidRootPart")

--// NPC
local NPCS = game.Workspace:WaitForChild("NPCS")


--// Functions
UIS.InputBegan:Connect(function(Input)
    if Input.KeyCode == Enum.KeyCode.X then
        if Chatting == true then
            Next = true
            Sounds.Click:Play()
        end
    end
end)

UIS.InputBegan:Connect(function(Input)
    if Input.KeyCode == Enum.KeyCode.Z then
        if Chatting == true then
            Exit = true
            Sounds.Click:Play()
        end
    end
end)

UIS.InputBegan:Connect(function(Input)
    if Input.KeyCode == Enum.KeyCode.E then
        print("E pressed")

        if Detected == true  then
            local Lines = DetectedNPC:FindFirstChild("Lines")

            local npcName = DetectedNPC.Name 
            LineLabel.npcname.Text = npcName --Displays NPC's name in dialogue GUI

            local npcImage = DetectedNPC.NPCImage.ImageLabel.Image --NPC's image that will be displayed
            LineLabel.ImageLabel.Image = npcImage
            LineLabel.ImageLabel.Visible = true

            if Lines then
                Sounds.Click:Play()

                Chatting = true
                Detected = false

                LineLabel.Text = " "

                PromptLabel:TweenSize(UDim2.new(0, 0, 0, 0), "Out", "Linear", 0.2)
                LineLabel:TweenPosition(UDim2.new(0, 0, 0.75, 0), "In", "Linear", 0.2)

                wait(0.5)
            end

                for i, Line in pairs(Lines:GetChildren()) do  --DON'T FORGET TO REMOVE TEST PRINTS


                    local Text1 = Lines.Line1.Value --Line1 StringValue

                    local Text2 = Lines.Line2.Value --Line2 StringValue

                    local Text3 = Lines.Line3.Value --Line3 StringValue

                    local sentenceArray = {Text1,Text2,Text3}

                    for j = 1, #sentenceArray do
                        print("lines: " .. #sentenceArray)

                        for i = 1, #sentenceArray[j] do --
                            LineLabel.Text = string.sub(sentenceArray[j], 1, i)
                            print(LineLabel.Text)
                            Sounds.Talk:Play()


                            if Next == true then
                                Next = false
                                LineLabel.Text = sentenceArray[j]
                                break
                            end

                            if Exit == true then
                                LineLabel.ImageLabel.Visible = false
                                break
                            end
                            wait(0.07)
                        end                                 

                        if Exit == true then    --Pause & wait
                            Exit = false
                            break
                        end
                        repeat wait() until Next == true or Exit == true
                        Next = false
                    end

                    Exit = false
                    Next = false
                    LineLabel.ImageLabel.Visible = false

                    PromptLabel:TweenSize(UDim2.new(0, 0, 0, 0), "Out", "Linear", 0.2)
                    LineLabel:TweenPosition(UDim2.new(0, 0, 1.2, 0), "Out", "Linear", 0.2)

                    wait(0.5)

                    Chatting = false
                    Detected = false

                end
        end
    end
end)