My self worth was non existent for many years, so I can understand your insecurities. I'll give a little back story that maybe will help us relate. I never went out with someone I actually wanted to go out with, I usually went for those that were available. This was because I didn't feel like I was worth anything and didn't think that what I wanted was important, so if by chance someone was interested I would take the opportunity. You might be different in that aspect but the insecurities are the same.
You feel like this person is someone who gives you self worth cause they are with you, and the thought of losing them frightens you because then you'll lose that confidence that you gain from being with that person (FYI, I'm speaking in theory). Losing this person in general is also scary because you genuinely care for them as well and the pain of being rejected is huge in your mind. The way that I worked through my insecurities is learning how to gain approval from myself. Paranoid thoughts about someone leaving you reveals a sense that this person defines you, makes you who you are. You have to learn that no matter if the person is in your life or not you will ALWAYS be OK.
The reason being is that you seek approval from one person in this world and that is YOU. You need to focus on taking care of you. That's how you gain confidence and security by giving yourself what you need whatever it might be. By doing this you'll more than likely gain more attention from your bf because people are draw to others that have a strong sense of who they are and what they want so he'll be inclined even more to be with you. but even if he doesn't stick around forever he doesn't define you, he doesn't give you worth. No one can give or take away who you are except you. Life is so much more enjoyable when you learn what you want and gain approval through yourself, the great thing about it is YOU NEVER HAVE TO SEEK IT OUT.
It's always with you, and you can just enjoy a persons company because you know whether that person is in your life or not you can enjoy life because you define yourself and no one else does. Really, seeking approval from yourself will bring you closer to your bf. You could drive yourself crazy worrying if he's gonna cheat on you or leave you, and I understand why it bothers you so much. You've felt that pain before, it's familiar to you and you don't want it to happen again. I'm gonna share a post with you from a member on this forum that goes by the handle delilahking. It helped me not to dwell on the past so much and to forgive what has happened to me in life so that I could take the necessary risk I need to take in order be happy with someone.
Don Henely said it best "there are people in your life, who've come and gone they let you down, you know they hurt your pride.
You better puy it all behind you, because life goes on, you keep carrying around that anger, it'll eat you up inside!"
(heart of the matter by Don Henley)
the only justice is the ability to forgive the past (not just the people involved) things that have been said and done may make you cringe and try to re think the why's and hows but all your doing is allowing it to continue eating at you. Now I'm all for learning from ones mistakes but it's time to let yourself graduate with honors and be the bigger person-start by forgiving yourself, after all-you are your own best friend and I think that's what best friends do best.
pat yourself on the back for getting away from the bad apples but don't let it spoil you to the whole tree.
I'm seeing someone now and I don't think it is something that is going to bloom into anything spectacular and I don't expect this person to be mine forever, but I'm OK with that. Completely OK and we're having fun together and that's whats most important. Have fun together, don't worry about what could happen. Take care of yourself, and enjoy what you have while you have it. Life is so spontaneous, and you could get what you want out of this. You never know for sure, but when you seek approval from yourself, you always know that you'll be alright, ALWAYS!