Why can’t I commit to her?

How will I know if I am ready for a serious commitment with someone? I am 30 years old and have been dating a 28-year -old woman for over three years. She thinks we are serious and believes I will marry her, but I have always struggled with the idea. I had four relationships before her, all of which ended because I thought there was someone better for me. I love my girlfriend and am convinced this relationship is great, but I still can’t bring myself to settle down with her. My worry is if I get engaged and change my mind, it will be devastating for her. I don’t want that to happen. How do I get over this fear?
If you need time, ask for it. If you believe you will hurt this person, don’t commit. The fear of settling down is common, and a certain amount of doubt is inevitable when it comes to making potentially life-changing decisions. You have had three years to think about this though, and must acknowledge that there is a real person who must be taken into consideration. Relationships are also partnerships, and sharing your doubts makes them easier to manage. Try talking to your girlfriend about your fears, tell her why you are concerned about a future with her, and give her an opportunity to explain why she believes in it. If she can’t convince you, and you believe you are incapable of putting in the work, you must also be prepared to accept that you are okay with not having this person in your life.

I broke up a month ago and my ex says its best if we don’t speak to each other anymore. I believe communicating is best for us both, but he is adamant. How do I get him to change his mind?
The end of a relationship will have a different impact on you both, and he is presumably doing what he thinks is best for his mental health. Why deny him that option?