1.) What's the best thing about being single?

It's all about you. You can do whatever you want with whom you want. You can pursue hobbies, go out with friends, flirt with as many people you like etc.

2.) Has anyone been in a string of unhealthy relationship's and what did you do to ensure that your next one isn't the same?

Often people end up in a series of unhealthy relationships because they're insecure, have low self-esteem etc. Hence, it might be worth to think about how and why you chose your last few partners. If you can't, maybe consider a few sessions of counseling. Furthermore, have a look at the site loveisrespect.org

3.) How can be a better man?

By becoming the best version of yourself. By looking after yourself and make sure that you're in a healthy space mentally and physically.