I have read somewhere and heard from so many friends and people that if we leave bodybuilding after certain years it might bulge or body and etc. Is it true?
I think what you may be referring to is that when you build extremely large muscles, and then fail to maintain them (so they shrink back to normal), the skin around them may appear stretched. The same happens for pregnant women, or obese people who lose a lot of fat. Obviously the skin will appear stretched afterwards, and may never become as tight as it once was.
That said, you only have to worry about this phenomenon if you plan to grow your muscles to positively gigantic proportions. If you simply build your body to look strong and masculine, but not exactly like the Hulk, you won't have anything to worry about. If you do want to look like the Hulk, I fear you'll have to live with some sagging if you ever abandon your training completely.
If by "bulging" you mean "getting fat", I think it only happens if you stop bodybuilding and neglect to adjust your diet to your new lifestyle. In this case you end up eating far too much for what your body really needs, so you can get fat because of that.
But muscles cannot "transform" to fat. They are totally different types of cells.