Should we get back together?

How do I know if I should take someone back after a relationship failed the first time? My ex-girlfriend believes we should give it another try, and 
I am tempted, but also worried because we didn’t resolve any of the issues that led to us breaking up in the first place. She thinks we can make it work if we are serious about this, but I keep wondering if that means she didn’t take it seriously the first time. My friends think I am making a mistake because they saw how unhappy I was, but I think we had some good times together which is why I don’t know what to do. How can I be sure this will be better a second time around?
How is anyone supposed to know if a relationship will work the first time, let alone the second? If you are aware that unresolved issues exist, it makes sense to address them first before committing to another attempt. Ask yourself if you want to be with this person and talk about why it didn’t work the first time. There’s no reason why you can’t make it work if you are committed to it, but that can only happen with honesty and clarity about what you are both doing. If you are confused, ask for time, keep meeting, and talk about the relationship as much as possible. If she believes in giving it another go, she should have no reason to wait until you are on the same page and feel more comfortable with the idea.

A few days ago, my boyfriend and I had an argument, and he abused me. My friends found out about this and think I should leave him. He has apologised repeatedly but I don’t know if what he did is reason enough to end our relationship. What should I do?
Go by his actions rather than his words alone and acknowledge that we all make mistakes when we are angry. You can leave if he does it again.