spreading out is difficult... i cant help but fear losing her if i try anything like that. i feel like her leaving could happen at any time, and that causes me to second guess everything.
This is definitely familiar to me -- it can be hard to build other emotional supports when you fear that turning your energy away from your partner might hurt the partnership somehow. It sounds like building other safe places could help in a lot of ways, though, even if you do so slowly. It might help with feelings of clingyness, with fears of not having emotional safety outside of this person, etc. Which is not to say that you can't continue to enjoy the joys of your relationship -- it could just give you an extra place to go for comfort! I agree with Mo and Sam that it would be great to make time to talk about that with your therapist, if you're able. We can also talk through some of that here, if it's helpful.
How does spending time on your own feel? Do you like to recharge alone, or do you prefer to be with your partners? I've found that when I'm having trouble seeking fulfillment outside of a primary relationship, it helps to just start with trying to enjoy time with myself.