Hi there, I am currently going through a very similar process. I have always let others define who I was, or I have rather copied them as I had no idea what type of behaviour was my own and what things did I like by myself, not because of the others. And as Im going through with it, I feel like the only way (at least for me) is to try anything you can and find out what you dislike, rather than what you like - because anytime I feel like I like something, I can never be sure if its really true or if Im just projecting my friend into it or if I just have a happy memory connected to it and so on. But as bpd goes often along with other conditions such as anxiety or depression, it can be so very hard and exhausting to get up and actually do it. This depends on your personal situation. But maybe now that you have somebody supportive on your side, you could use it and talk to your partner and try to think of ways he could help you find new things, maybe introduce you to some of his favorite activities and so on. Just bevare, its a really long run and it will take time. So be patient ❤️ And if you ever wanted to talk about it deeper, feel free to send me a message, it might feel nice to have somebody who is going through the same thing 🙃