I think you are over-thinking this. At 17, it’s a little early to be talking about what you’ve “always” done in relationships. I don’t think what you’ve been doing has anything to do with the “thrill of the chase”. It’s more likely that you’ve been doing the normal exploring of relationships that goes on in the teen years.
Make no mistake: Finding the right person and making a healthy relationship is a big challenge for everyone. Most people develop some crushes first. Most people “panic” a few times when the crush (from a distance) actually returns the interest. Once people become more self-confident and more socially skilled, they become more able to explore a real up-close-and-personal relationship.
Your relationship with your cousin when you were a kid was an early experiment in romance. This is common and normal. Often young people develop a crush on an older person in the family who is warm and friendly. When we were talking about this one day, one of my psychologist friends joked that his six year old boy wanted to marry his mom while his 3 year old daughter wanted to marry her brother. This is not cause for alarm! The kids were sorting out what loving and relationships are about. Being children, they thought that when people love each other, of course they get married.
The process usually goes something like this: The child looks for affirmation that he or she is lovable. The parent reassures the child that he or she is attractive and interesting. What makes this safe is that the parent is absolutely clear that parents are parents, not potential partners. It is in the safety of that exchange that kids begin the process of seeing themselves as someone who can find a partner someday.
Your cousin probably pushed you away when you were a tween because, with 4 years between you, he realized that giving you hope of a relationship with him was inappropriate. He may have “panicked” at the thought. That tells me he has a healthy sense of boundaries.
Please give yourself time. Did you know that almost 40% of teens don’t date at all? These young men and women aren’t losers. They simply aren’t interested in the drama of the high school dating scene. Instead of pairing off, they are more likely to have a group of friends they hang out with. They feel ready to look for love when everyone is a bit more mature. Most are successful in finding romance after graduation — either at work or in college.
Please relax. You have plenty of time to find love. Meanwhile, enjoy your friends and be active in something that matters. The rest will unfold naturally.
I wish you well.