Keep your past & future in your life as working office and vacation resorts but not as your home. The present is your home.
You earn money at your office, similarly you learn from your past. You leisurely spend your holidays at vacation resorts, similarly your dream better for your future. But you actually live at your home with your family, friends, your living, your hobbies, your fun, everything, your life, which no one forces you to do or which you need to do because of some compulsion. But what you do naturally, with a life rhythm without thinking anything just being relaxed naturally. At resort, you go with a need to relax, but at home you are always relaxed.
Now, think if you have to spend 18 hours at office and you are not coming to home for weeks. Or, if you have gone for a year long vacation. Then these places will eat you up, you want to run to your home.
So, be at present, live in present. Go to past to learn & come back. Go to future to dream & come back.
Happiness is relative when you compare with past and future.
Happiness is absolute when you are just happy.
How to be in present moment ?
Keep your mind where your body is.