The first thing on your mind when you think about your old flame is likely what are their intentions and do they still have feelings for you. It can be very easy to just go with the flow and let things happen but you should really take a step back and see if this is going anywhere.
It is vital that you don't kid yourself and just simply be honest... if the signs don't add up then it's probably just a fling.
Be careful when someone says that they have changed. It is one thing to say it, but another to actually prove it through actions. I am not saying that you shouldn't give them a chance to show you but don't just believe them because they say so.
The good news is that people learn through their experiences. And if you both have dated other people but end up with each other again then it's likely you both are more mature and the relationship has more potential this time around. That old saying that "people can't change" is a myth... and an oversimplification of the human psyche. People don't always make the right choices the first time around but we definitely learn as we go, so don't be afraid to test your exes feelings as well as your own. It is absolutely possible that they are for real.
The first step is to gather your thoughts and feelings. Second is to make sure they are for real and test them by making them back their words with actions.
The third and final step is to TAKE IT SLOW! If you rush back into the relationship where you left off then what path do you think you're still headed on! That same heartbreak train wreck you already experienced. When I say take it slow, i don't mean sleep with them whenever they want and then try to date them. I mean treat them like they are on probation and they must prove themselves to you before you will let your feelings out. Believe me letting your feelings out to fast too soon will not be good and you will essentially be creating a false environment where you can't possibly hope to discover the truth about your ex's intentions. Obviously if they lose interest because you don't do everything they want or don't sleep with them immediately then their actions speak for themselves regardless if they say they have changed.