Hey @Yddek,
I think everyone struggles with these kinds of thoughts! You are not a bad friend for worrying and you probably shouldn't be trying to push these thoughts away (trying to push away thoughts often makes them stronger in my experience!). However, seeking reassurance a lot or accusing your friend of not wanting to be your friend might make her withdraw or not want to make you jealous by telling you she's spending time with others.
I totally understand what it's like not having many close connections
and the anxieties that come with a new friendship especially when you don't have many other people you can rely on. My advice is to just be yourself and don't worry about how long you'll be friends, just enjoy it while you can. It will ultimately help you down the track to make more connections and understand yourself better (what you value, etc.)
And there's nothing wrong with telling a person you value their friendship, maybe just don't overdo it or they'll get suspicious 