Severe Relationship Anxiety/Insecurity

Does anyone else suffer with this? I analyse every single thing he does/says and work myself up into a complete state most days. I'm constantly worried my partner will leave/find someone else. I have just started some therapy to try and help but I'm driving my partner away and could use some support/advice. It's at the point where ALL I think about is him and my worry is constant. It's affecting every aspect of my life and I'm finding it difficult to concentrate at work and haven't eaten properly in over a month (I go days with nothing or at most some fruit or maybe a piece of cheese etc). Anyone with any tips on how to stop these obsessive and unfounded thoughts would be a great help. My partner is backing away and being distant now because he is fed up so that makes me worse... Catch 22 situation and I have no idea how to change things and get back to the happy couple we were 😢