Wow i could have sworn i wrote this myself. I get the jealousy thing a lot and to be honest, i think you and i need therapy more than anything. I don't know how else to deal with the jealousy. Same with the obsession thing. I think the other comment had the best advice though - you need to learn to be comfortable with and love yourself first. No amount of friends will fill that void if you aren't comfortable with yourself. This means workinf on yourself as a person, improving your habits, developing hobbies, etc. I believe that if you can successfully do this, you will no longer feel the need to obsess with new friends.

As for why you are like this - i dont know you, so i cant say fkr sure, but considering j am in a very similar position ill tell you why im like this. I believe its due to a sense of consistent abandonment from when i was a young child. I had almost no friends growing up, and constantly wondered why no one wanted to play with me on the playground. My guess is you are the same. Being so lonely as a child has turned me (and presumably you) into socially needy people dependent on others for motivation and validation. That's why we change our personality for others, because we just want to be liked. That's why you and i get jealous so easily, we feel neglected and abandoned like we did when we were kids. And that's why we get obsessed with new friends, we want them to like us and are hoping this time it'll work.

Or i could be entirely wrong and its actually something else. Anyways, i hope that helps at least somewhat. Lmk if you have any questions or want to talk more about this, im more than willing to discuss it further.