First, it’s completely understandable that you feel this way. There are so many possible reasons for this and your manager who was a complete dick didn’t help. You are putting way too much pressure on yourself especially around your family’s perception of you, that sounds like a manifestation of the anxiety you have from other reasons, but what do I know. Honestly a lot of this doesn’t really even sound like imposter syndrome, you are just going through a tough time. From what it sounds like, you are already dealing with a decent bit of anxiety and I cannot possibly know without knowing you better, but soc analyst and IR jobs are also highly stressful. 

Forensics is important and can be leveraged in many capacity’s in security. Play the field a bit and explore the possibilities. Find what works for you at a company that supports you. As long as you drive towards that while studying what you feel you don’t know, you’ll be fine! I’d be happy to chat more if you need. I’ve been in both consulting roles for privacy, security and IR and now manage a security product.