You have been thinking about an ex. He is now in your life and you are thinking about giving him another chance. Before making that big step think about some things.
The first thing you should think about is that there is a reason why you broke up. If it is because you had to go to separate schools then that's different. If it is because he cheated on you, abused you, was mean to you or whatever bad reason then you should think twice about giving him another chance.
The second thing you should know is that people don't change. If he was immature when he was 18, he matured when he is 30 (hopefully). If he was mean or a player than he won't change. Yes players do stop playing once they meet the right girl but you don't know if he changed. If he hurt you once most likely he will do it again.
The third thing you should do is ask yourself: Why am I giving this person a second chance? Is it because you are comparing him to the guys you know who aren't giving you a chance or is it because you really love him? If it is love and you feel it has potential go for it. If it is because you have a fear of being alone, then you are settling and it is wrong.
The last thing you should think about is trust. Can you trust that this person will not hurt you? Is the love you have in your heart for him worth getting hurt? If you have a feeling he will hurt you again, then you shouldn't give him another chance. Once again if he hurt you once, he will hurt you again.
Weigh the pros and cons. If there are more pros than cons then go for it. Sometimes it is all about timing. If there is doubt then maybe he isn't the guy for you. Keep moving forward and never give up. The right guy is out there for you. So focus on the new and not the past.