How else can i stay on my diet?

I need encouragement!
So after years of yo-yo dieting, I've hit an all time low and spent the last month and a half starving myself. Sure, I lost a good 20 pounds, but I also lost my energy, tolerance, and my period. When I came to my parents house for...

the weekend, I realized this was unrealistic to keep up any longer.. I had quite a binge on things I never let myself eat. I've decided ONCE AND FOR ALL to live the healthy way, with breakfast lunch and dinner, no snacks (well, every once in a while), and regular exercise (im starting cardio boxing classes tuesday, and also spinning, and running plus HIIT)
I am expecting to gain a little at first... and then lose a bit or at least tone up at where I am. Is this a good expectation?
I am excited to finally live a lifestyle that has a realistic possibility of maintaining life-long weight control. But I know as soon as my body starts to change at first (since I lost all that weight and am now starting to eat again) that I'm going to question whether or not I should relapse to my former lifestyle.
Words of encouragement please!!
especially from anyone who has done this change before

Also, what are some good healthy weight-loss aiding foods to buy for when I go shopping?
I've been googling (ha) and so far I've found
Grapefruit
Sardines
Canned Pumpkin
Yogurt
as must-haves. Obviously there is much more to learn! But these are things that are supposed to be like hidden gems or whatever. I'd appreciate any other tips you guys have!

um just buy lots of fruits and vegetables, and believe it or not, eat meat(protein), and its also ok for you to treat yourself to dessert or else you will just like quit the whole diet thing, because you miss the treats so much! I am doing all of things I said in this, and I lost 10 pounds in like 2 weeks

I eat grilled chicken breasts(or other lean meat) and vegetables and brown rice and drink lots of water. just keep it light, dont over eat, exercise frequently. you sound like you are off to a good start keep at it.

The no snacks policy is a bad one.

Instead of eating three big meals a day, eat six smaller ones.

What is HIIT?