If you got fucked over, fuck them. Don't contact them, don't waste your time to be disappointed as you will be. Well done for making that decision, as I assure you it's the right one.

Don't bother fighting why cause yourself unnecessary stress? Start using that time to get together with old friends, go out more, work out at the gym or just start lifting weights. I couldn't eat for ages after my experience and lost a load of weight, once I started to pile that back on it was muscle instead.
I understand that probably sounds harsh, but said it once and say it again don't mug yourself. It took me a few weeks to realize that and I wish I had known it from the beginning, but we all learn from experience. So for whatever you might consider a mistake you made a few weeks down the line don't blame yourself for it. It's normal to feel lonely, some people, such as myself just have the want for a person around all the time and it's a massive change to go from that to not. Whether I was in a relationship before or not, if I was sitting alone for long periods of time I'd feel lonely. Remember to consider that, as it took me a good few months to click onto that and I wish I had sooner. I didn't miss the person, I missed the comfort of a relationship/'companion'. Of course some people out there, (think the likes of Spade possibly but not 100%) are the complete opposite.
Hope things improve, it goes up and down and whatever you do
don't touch benzos. I swear to fuck, seen it happen with others too, they make the whole 'single' thing feel worse by 1000x. If you saw the likes of my posts when I've been coming off them and been at complete rock bottom, in comparison to how I feel when I'm not on them and have a sober perception on things its insane. To the point were I've had to go back and edit posts. People I know who have ignored this advice seem to take much, much longer to get over the relationship.
Cycling was a real good one for me, headphones in, cycle about head is cleared and good exercise. Only problem is the snow/weather here at the moment has stopped me being able to go for a run/cycle. I'm not much of a gym guy myself. Sleep lots too - not drug induced though.