Sorry to hear that, mate. I can totally understand what you might be going through, but I think it would be a terrible idea to "convince" someone to be in a relationship with yourself. To be honest, it would be best not to get back together even if she changes her mind in the near future. You deserve someone who wants to be with you, not someone who you need to convince to not leave.
There could be so many reasons why someone might not want to be in a relationship with you, and a lot of the time, it could have nothing to do with you as a person. Sometimes people just "feel" things are not right and act on it. I'm sure you must have taken some decisions following a similar line of thought.
It's normal to have questions and ask for a rational explanation for such events but it's never worth the effort. Sometimes a rational explanation doesn't exist at all but even when it does, it's unlikely that you'll see it in the same light and therefore it would most likely start an argument than give you closure.
"What are the next steps?" Well, I'm glad you're keeping an open mind and looking for suggestions. In my opinion, you could do the following:
1. Accept that it's over and realise that you both got a lot to learn from this experience. Realise that sometimes people are just not compatible and one of you sensed it before the other.
2. Be grateful that this experience changed you as a person and now that it has run its time, you should look for other experiences that would help you develop as a person.
3. Get off the relationship wagon for a while. Do not think about getting into a new relationship (or getting back with your ex) unless you feel like you're neither mad about the events that happened in your previous relationship, nor are you looking for any answers regarding your previous breakup. This will take time, allow it. Do something else in the meantime, maybe a hobby or hitting the gym would help.
4. When you've come to terms with your situation and you are no longer expecting your ex to get back to you, open up to some friends you trust. Tell them how you are trying to move forward with your life and be open to their suggestions because chances are, they will have some.
This text turned out to be longer than I expected, sorry about it. I hope it helps though. Apologies if anything comes off as a bit offensive or condescending, no attempt was made to make it sound like that. This is my take on your situation, someone might have a completely different opinion so take from it what makes sense to you and bin the rest. It's important to try ideas out and see what works best for you.
On a final thought, I think it's best to treat your girlfriend just like you would treat your girl best friend. Nothing wrong with making her feel like a queen a couple of times a year but it's uncomfortable to be treated like that on a daily basis. I hope this makes sense.