That sounds really tough. I'm very similar to you I think, except neither my boyfriend or I have any friends really at the moment. I know I would feel insecure too. Anyway, it sounds like this is something you bring up with her a lot, and you likely have arguments because you feel threatened and as if you need to protect yourself. I wonder if you could approach a new conversation from a problem-solving stance and tell her you want to work on your insecurity together, but that it might be helpful first for you to hear in her words what she loves about you. Maybe you're not sure what she sees in you? I'm wondering if just hearing that will give you something to hold onto to remind yourself of when you're having a rough time.

Also, then you can practice taking your fears and really digging deep and analyzing whether there is evidence to support them, or evidence against them. It can be a very vulnerable and painful feeling to take a leap of faith and trust in someone's love for you. Another idea I have is to have a conversation about what you need from her to feel loved. Is it words of affection? Physical touch? Quality time together? It might be helpful if she shows the particular kind of love that you need.