This resonates with me so much. I have a number of very close friends, and I care deeply about these friendships. When I opened up to one of my friends about being aro/ace, she expressed how she knew I put a lot of value in my friendships and have always cared a lot for my friends. It made me wonder if maybe I was more invested in my close friendships because I have never wanted anything more than friendships, so these relationships are very important to me, in a way they might not be as important to someone who also has a romantic partner to rely on for emotional closeness.
I also get what you mean about stability, and I felt like that too for so many years. I think the reason I have always invested in multiple friends, rather than just having one best friend, is because there is not the same kind of commitment assumed in friendships, so if a friend's life takes them in a different direction (e.g., romantic relationships, moving for work) then I still have other friends to fill that need for friendship in my life. That being said, I recently bought a house with one of my friends and her husband, and I have noticed that this has kind of brought this friendship to the forefront of my other friendships. For the first time in my life, I feel like my future is actually connected to someone else's, and I can have conversations with these friends about mutual goals for the future, which wasn't really something I would say happened in other friendships. I also find that I have become more emotionally intimate with this friend, and perhaps less emotionally invested in other friends since we bought the house together, and I think this has a lot to do with the feeling of permanence and commitment in this relationship.