I poked around through your source code, and I have some advice:
1. Don't define a global header file like you did. Have bool isRunning contained within a class, main.cpp, or pass it around as a parameter. It's bad practice to keep global variables.
2. Instead of having a textures() or init() method, initialize from the constructors of each class. You did this on game.h and menu.h.
3. In general, your draw() methods have a lot of things that would be better suited under an update() function or similar. Things such as looping through conditions and setting strings, etc.
4. You drew things in methods other than draw() like tie() and lose(). You should keep all the drawing in one place.
5. Great job on your first game. Keep practicing and learning C++!
