Why am I so afraid of being alone, and what can I do to like myself more?

I am very much an extrovert. I feel best when I am with other people in social situations. I realized recently though that I am actually terrified of being alone. I have started multiple relationships because of this and I believe those are the wrong reasons to start relationships. I hate being alone by myself and when I am, my thought process is often negative and self-deprecating, so I think that self hatred may be the root of the problem. I never thought of myself as someone who hated themselves and am normally quite a positive person full of affirmations and good vibes, but I am not that way, usually when I am alone. I feel like I need other people to validate my existence. Why am so afraid of being alone, and how do I stop?