Reddit mentions of Love Me, Don't Leave Me: Overcoming Fear of Abandonment and Building Lasting, Loving Relationships

It sounds like you probably have an Anxious attachment style, and unfortunately LDRs can be extremely difficult for people with that attachment style - so please be kind to yourself. You're not selfish or useless, and you're in a tough situation so your feelings are understandable. If you can afford it, I'd definitely recommend therapy. But if not, do your best to find some good friends who can support you. I've also found EFT tapping very useful for dealing with overwhelming feelings, so it might be worth trying as you can learn it online for free here: EFT tapping

I'd recommend checking out 'Attached' by Amir Levine and Rachel Heller, as well as 'Insecure in Love' by Leslie Becker-Phelps.

I found this book helpful: Love Me, Don't Leave Me: Overcoming Fear of Abandonment and Building Lasting, Loving Relationships

Another one specifically about jealousy is 'The Jealousy Cure' by Robert Leahy.

This article is also a good starting point: How Your Attachment Style Impacts Your Relationship

It sounds like you probably have an Anxious-Preoccupied attachment style. If you can afford to see an attachment focused therapist, I'd highly recommend it. If not, consider checking out the following books as they have a lot of great advice about this:

Attached by Amir Levine and Rachel Heller

Insecure in Love by Leslie Becker-Phelps

Love Me Don't Leave Me by Michelle Skeen

I've also found EFT tapping to be a very useful technique for reducing anxiety and managing difficult emotions, and you can learn it for free online.