where is the memory leak here relating to texture2d?

Solved! As @Athanasios Kataras suggested, making the variable persist solved the problem. I had actually tried to make it persist before, but it did not work. I only now remembered that I did not actually save the file.

Here is the reworked code:

public float height = 10f;
public float width = 2f;
public float defaultSpread = 10f;
public Color color = Color.grey;
public bool resizeable = false;
public float resizedSpread = 20f;
public float resizeSpeed = 3f;
[SerializeField]
float velocityMin = 210;

float spread = 0;
bool resizing = false;

CharacterController player;

Texture2D texture;

void Awake()
{
    //set spread
    spread = defaultSpread;
    player = GameObject.FindGameObjectWithTag("Player").GetComponent<CharacterController>();

    texture = new Texture2D(1, 1);
    texture.SetPixel(0, 0, color);
    texture.wrapMode = TextureWrapMode.Repeat;
    texture.Apply();
}

void Update()
{
    if (player.velocity.sqrMagnitude > velocityMin) { resizing = true; } else { resizing = false; }

    if (resizeable)
    {
        if (resizing)
        {
            //increase spread 
            spread = Mathf.Lerp(spread, resizedSpread, resizeSpeed * Time.deltaTime);
        }
        else
        {
            //decrease spread
            spread = Mathf.Lerp(spread, defaultSpread, resizeSpeed * Time.deltaTime);
        }

        //clamp spread
        spread = Mathf.Clamp(spread, defaultSpread, resizedSpread);
    }
}

void OnGUI()
{
    //up rect
    GUI.DrawTexture(new Rect(Screen.width / 2 - width / 2, (Screen.height / 2 - height / 2) + spread / 2, width, height), texture);

    //down rect
    GUI.DrawTexture(new Rect(Screen.width / 2 - width / 2, (Screen.height / 2 - height / 2) - spread / 2, width, height), texture);

    //left rect
    GUI.DrawTexture(new Rect((Screen.width / 2 - height / 2) + spread / 2, Screen.height / 2 - width / 2, height, width), texture);

    //right rect
    GUI.DrawTexture(new Rect((Screen.width / 2 - height / 2) - spread / 2, Screen.height / 2 - width / 2, height, width), texture);
}

It is still running in OnGUI because I am using GUI functions, and also because I get 400 fps when this game is running, I really don’t need to spend the time to edge out a tiny bit of performance.