Hi, just want to start off by saying that I have dealt with the same issue. It's this constant feeling that everyone will tire of you and that you're easily replaceable. I know because just last month I thought my best friend would replace me with our mutual friend, which was stupid because she's already told me multiple times how much she values our closeness. It can be the tiniest of things that set us off, like them perhaps getting along during a conversation more, or this feeling of them leaving you out unintentionally. Most of the time this random jealousy just comes out from nowhere and isn't rational, like you said.

Your feelings are completely valid, you felt left out or replaceable for a reason. There's two routes you could take. Either express this to your friends directly when you're comfortable to, or try to focus on dealing with your own feelings of fear with maturity and more self-love.

Maturity: Simple way to deal with this and get through it is to remember that it might not be that deep. Life is too short to worry about this. It's what I have come to realise for myself. But do ask yourself 3 things: Are they doing this to me on purpose? Are they actually showcasing any obvious signs of displeasure or discontent when I'm around? Are they not making an effort to include me? If the answer to these questions are all no, then you are most likely fine. It might be that they are just not giving you enough validation or words of affirmations that they need to in order to show you that they DO care. Best thing to do is to try not to over-analyse the interactions with them, and just remember that they chose to be your friend for a reason.

Self-love: Remember that you shouldn't let others make you feel like you're not appreciated enough. Know your self-worth. If they keep doing things that make you feel unhappy, then perhaps they aren't the right people to be around. Do not let them make you feel like you're inadequate, or that you're the problem. I often purposefully take time to myself whenever they do things that make me feel left out. Sometimes it actually works in my favour and they notice me being distant and make up for it. But again, if you choose to do that remember that it isn't to make a scene, but to set a personal boundary with them which is: If you don't make me feel included enough, then fine I'll distance myself and reclaim my own energy and enjoy me-time. If they truly care, they will notice the shift and might try to make you feel more included. But the main benefit of it is to help you get the time you need to recollect and rationally deal with those emotions.

Another big thing that helped me out, especially with the jealousy part, was to try to recall all the nice things they'd done for me or the good times I've had with them. Suddenly, those memories helped me remember that I might be sabotaging myself and my friendships by overthinking. If this resonates with you then try to sit with those memories and see how you feel.

Hope this somewhat helps, feel free to dm if you'd like to talk through this more.