I can't comment on the first bit, but the second bit will only ever be as hard as you make it yourself.
Making simple changes in life is easy and effective, and lead to changes on a larger scale. You said you've put weight on and that's reduced your confidence; change it. Instead of a chocolate bar, eat an apple. Instead of half an hour on facebook, go for a quick walk. In conjunction, nature and activities that exert you have been proven to be brilliant natural anti-depressions.
Yoga and meditation also helps. I do half an hour yoga before bed and usually meditate for once an hour every other day. These allow me to properly focus on myself and what is currently bothering me/how to fix it.
Also, find happiness in your own worth. I'm not saying you don't have that, but you mentioned you've been getting clingy. Not only is this an unattractive quality but it's also a sign of being emotionally unhealthy. There's not a single second where I think '****, I wish x was here to spend time with me' when I'm on my own, because I'm perfectly content. I can't tell you what your own past times should be, but I deeply deeply believe every single soul in the world needs to be at peace with themselves before they engage in any sort of relationships, friendship or romantic.
People are meant to compliment your lives and not dominate them. Take this time out to focus on you, your health and your passions and re-visit the idea of going back to him at a later date. If it was meant to be, it will be, so relax and focus on you.
, No change is too difficult and, as stereotypical as it sounds, you can change yourself for the better at any given moment. It depends entirely on how determined you are, and I think everyone has enough determination in them to change themselves for the better.