When I realize I'm in a can't win situation squeeze, I "give up" both sides. If you feel he is going to abandon you no matter what you do, like the Cheshire Cat tells Alice, it doesn't matter what you do.
So pick something interesting to experiment with. Be bolder/braver about expressing your feelings and see what happens. See if you can pay attention to the other person's response to you rather than just your own fears. Fears are often about "future" events; if you can learn to stay in the present, when your boyfriend is reassuring you and caring about you, that could be nice for you?