Here's something that needs to be said.
Building a lean and healthy body is not going to make you happy.
Yes, it can definitely improve your quality of life.
Yes, it can make you feel good about how you look.
Yes, it can sharpen your mind.
Yes, it can lower your risk of chronic diseases like heart disease and diabetes.
Yes, it can improve your cardiovascular health.
Yes, it can lower your risk of several types of cancer (such as colon, breast, and lung).
Yes, it can help you to fall asleep faster.
Yes, it can build and maintain bone density and muscle mass.
Yes, you will like the way your clothes fit.
Yes, you will feel like a reasonably attractive person.
And yes, it will bring a certain level of satisfaction into your life that you didn't have previously.
I encourage you to be fit and lean. I don't know anybody who wouldn't want to be healthy and active.
But anyone who tells you that fitness will make you happy is straight up lying, just like making a lot of money won't do that for you or accumulating lots of "stuff" or arriving at the height of your profession or seeking self-worth through "likes" or viewing a new house or car as the ultimate finish line.
None of these external things is going to put you into some sort of permanent state of bliss.
If there's anything in life that is going to bring you lasting happiness or genuine satisfaction it's going to be the less obvious things like meaningful relationships or having a purpose in life or contributing to the wellbeing of others or walking with the Lord your God.
So go ahead and build the body you want. There's absolutely nothing wrong with that.
I myself work really hard at it and enjoy it. I get a feeling of satisfaction after every workout and marathon on a basic surface level.
But don't think these things are going to make you happy in the deepest sense. They can't and they won't.
Have a wonderful day!