b. Self-invest with flow activities.

I suggest self-investing because, right now, a large part of your identity is entangled with your feelings towards her. Self-investing means growing your identity means transcending your feelings.

I suggest flow because, if you pull off a flow state, you invest all your cognitive resources in the task you're working on. Meaning your brain is unable to think of anything else. This is incredibly valuable.

a. I'm coming out of a similar situation. A large contributor was the fact I wasn't meeting a lot of women. If your universe consists of two datable women, it's easy to obsess on one. If you're regularly meeting a lot of women who tend to have the traits you look for, that happens much less. May not be your problem, but what you've written sounds familiar enough that I'm going to go ahead and try other-optimizing.

If you haven't read it yet, this is generally helpful.