Start with something easy and establish a rule that won't ever be broken. If you break a rule once, you'll lose the fight.
My rule, for example, when I started to train more:
- start with 10 crunches every morning and evening
- increase by 2 crunches every day
- no exceptions
When you are at ~2 months in, you can add weight training to it to get stronger.
Additionally, find a sport that you can do once or twice a week that is FUN to do. By FUN I really mean it. There's no point in doing sports if you don't enjoy it.
If you enjoy playing batminton, go for it! If you enjoy table tennis, go for it! If you enjoy Kung Fu, Krav Maga, or whatever ... go for it!
Sports isn't about reaching goals, it's about having fun while doing it. Otherwise, you will not overcome the struggles. Your brain needs a reward, and enjoying sports helps you keep wanting more of it.
Since you said you went through three weight loss cycles (bravo, it is hard to do!), is exercise an important part of the effort? Example: Did you ever try cardio vs weight training? It seems like weight training is the more likely of the two to change body composition (more muscle, same or less fat). And higher muscle weight almost always leads to higher resting calorie burn rate.
Last thing that almost no one is talking about in this discussion: Once you start doing exercise, something changes in your brain. I cannot precisely explain it, but a huge number of men experience a drop is depressing thoughts after starting regular exercise. My guess: Exercise helps to de-stress which has all kinds of other positive impacts in your life.