It sounds like you're dealing with insecure attachment, working on building security and confidence in your relationship with yourself could help! The more secure and confident you feel about yourself, the more security you will have in your relationships. It's reminding yourself that you can take care of your own emotional needs and you'll be okay even if things in your relationship aren't okay. Therapy can be really beneficial. In terms of practical self-soothing strategies, when you're starting to feel anxious engage in some type of hobby you really enjoy, I find that meditative and repetitive motions are really helpful for me like coloring, making crafts with my hands, movement, and journaling. Do something you really enjoy by yourself to prove to yourself that you are your own good company and while you love your boyfriend you don't NEED him every second.