Stop demanding that he should give u all his time and attention because thats practically not possible. Even if he is developing feelings for that girl that doesnt prove that he considers u less or ignoring you. He has a power of choice and free will that everybody has and dont expect him to feel exactly the same way for u as u feel for him beacuse everbody has a different thought process and so feelings towards the same situation. Interacting with him is one way to feel happy and satisfied. There are so many other options for feeling reasonably happy like try to find more friends like him, pursue any kind of activity that u find absorbing, regular exercise , yoga, meet ur exsiting friends, etcetra etcetra. Psychologically Its not his hiding things thats making u insecure and angry but its ur own demand about it thats causing ur disturbance. Keep ur demand to a preference and respect his right to hide things without damning him.