Maintaining

I went down to 1500 calorie diet for 3 months lost 60 pounds, should i be worried about it all coming back?

The problem with losing too much weight too fast is that most of the time it is done with some extreme diet that does not change a persons eating habits. So once the diet is over they return to old eating habits and the weight comes right back.  Also extreme diets prime the body to store fat in case of future loss of food (i.e. another extreme diet). 

Should you be worried about gaining it back? That depends on what you do now.  If you have changed eating and exercise habits to something that can maintain your new weight, then you don't need to worry, just keep doing the new habits.  If yu have lost the weight so you can get back to your "normal" life then yes you will need to worry. 

I know for me I am learning new eating habits as I lose weight so that I won't let the weight come back.  I am learning about portion control, exercise, and healthy foods.  I am sure what I lose will stay off because I am continuing to track what I eat and how much.  This has gotten to be a heathy habit for me and does not take up too much time.  This new way of thinking and acting is beginning to be my "normal" which is what I want to do. No more diets, just constant heathy eating and exercising.

Congrats on your weight loss. Good luck on keeping heathy.  This site has tons of tools to help you keep on track.

I did the same thing for 6 months. When I finished losing the weight, my eating drifted back to where it was when I started. That's about 40% above my BMR, so I have to exercise a lot to keep the weight off. 700 extra calories per day equals 10 miles of walking.

Eating habits die hard. I am eating a healthier diet than I did before, but not any less calorie-wise. If I quit exercising I know that I'm eating enough to put 50 pounds back on. I know that I could do it quickly, too. I'm just coming off a spike of overeating/underexercising. It took 5 days to put on 9 lbs eating an excess 350 calories per day, and it's taken 5 days of 200 calories per day deficit to take 8 lbs of that back off. These gains/losses are due to water retention/digested food in the GI/temporary glucose storage, but if I hadn't resumed my normal eating/exercise they would have become fat again.

Yes you should be worried.   The term is 'yo-yo-dieting' and it's horribly common with crash dieters.   As previously explained, you may have significantly lowered your metabolism so any extra you eat is more easily stored as fat.   You could be one of the lucky ones who have managed to educate yourself to eat more healthily, enjoy smaller portions and do more exercise, of course.  But if you've just relied on 'not eating' and avoiding food to get you to this point then you should expect some gain as you start eating again.   You're quite young and energetic so you may be able to keep the gain down to about 1/3 of what you've lost.