First of all - Congratulations on the weight loss - to all of you. I know how hard you've been working and what determination you have. I also know really really well the fear you are facing. I was in the same place 12 years ago. My surgery was 13 years ago this month. I lost 170 lbs and have managed to keep it off - Yeah!
I was really afraid of re-gain those first couple of years - especially as my appetite came back. I've roller coastered a bit at times but have managed to stay within about a 15 lb range. Don't let the fear stress you out because that can act as a push into old eating habits. Here's a few things I did to help me stay stable.
I changed my eating habits drastically in that first year while I could. I cut out all sugar, went low on the grains, stopped all fast food with the rare exception, and went organic. It was easy to do that in the beginning when I was v. motivated because I kept thinking long term.
I set up good solid exercise routines - doing things I liked like biking, dancing, swimming and walking. I continued to do those things because I liked them. I didn't get on the treadmill or exercise bike because I didn't like them and knew I wouldn't keep it up. I also set up and have continued to do a simple weight training routine.
I got help when I needed it - used the professionals in my program but also went outside for psychotherapy and life coaching.
Lastly I worked hard at not freaking out when I did gain a pound or 2 or even 10! I'd just do an inventory of where I was getting slack - esp. with the rules of the pouch - and trusted myself to get back on track, even if it took me a few days or even a week. I didn't freak out, go into despair and start that downward spiral of beat myself up, eat more, beat myself up more, eat more, etc.
This is all simply put here but I put in a lot of work and time and continued vigilance yet learning to let go and enjoy life up to this day. I know I'll never gain back that weight. Good luck to all of you. The fact that you are concerned and looking long term is a great sign that you'll make it!