My boyfriend is insecure, how can I help?

[Butterlyalwaysxx]

Me and my boyfriend have been together for 1.5 years. We have broken up once due to the fact that he felt as if he wasn't able to make me happy and he left so I was able to find that person. He made me unhappy because I felt like I was being taken for granted and he wasn't putting a lot of effort into the relationship.
We got back together as he realised he made a mistake, and ever since he's been incredibly wonderful and never wants to make me feel unhappy or insecure, he also said that he never wants to leave me again.
Because of the breakup, he knew that it would be difficult for me to trust him that he wouldn't leave again, and I am having difficulties trying to believe him when he says that he'd never leave me again (because a week before we broke up he told me he'd never leave me, and he did). I do however know that he was incredibly miserable without me, and he realised the way he used to treat me wasn't good, hence why he's never treated me that way ever again.
Now we are back together, he's always scared that because he's left me feeling insecure (if he'd leave again), he scared that I'll find someone 'better', someone who doesn't make me feel insecure and I'd leave him for that other guy. (Obviously I'd never do that as I love him and I only want him, but he doesn't seem to realise).
Due to the breakup, he's left feeling insecure that I'll find better and leave him, and I'm scared that he'll leave again. The reason why is because whenever I tell him I'm scared he'll leave again, he starts to worry that because I'm insecure with him, I'll find someone that doesn't make me insecure and leave, so I end up feeling guilty for telling him when I feel insecure because I never know if he'll feel like I deserve better again and leave me.
What do I do?

Updates:

[JustBeingHonest7]

I think you need to tell him what HE can do to give you your security back. Don't bring it up, but the next time it comes up naturally maybe something along the lines of:

yes, I do feel very insecure in the relationship and I I do feel scared you will leave again. I think that I could get over this if you _________________" (example might be-proving he is trustworthy maybe by showing that you can trust what he says now. Like making promises and sticking to them. )

I also think that it may be helpful for you to own up for your own role YOU played in the relationship failing the first time. If he felt like he couldn't make you happy, then I have to wonder how often you showed him (cuz actions are more important than words to men) how much you appreciate everything he did to try to make you happy?

And if I'm correct in that guess, perhaps you can make sure you are showing him real appreciation and gratitude when he does all those little things for you now?

[StarlightSwift]

To be honest I don't think this relationship will work in the long run. Trust is such a vital part of a realtionship and this will just keep eating you both alive unless you can move past it but it is going to be hard

[Anonymous]

I know it sounds very cheesy but u are both in love so I get u could do it. My suggestion would be to write him a love letter. You could pour your heart out and say everything u want to say to him (the things u wrote here in your question for example) I think it will be easier for him to believe the things u told him when he sees them written down on a piece of paper.
I don't know u guys so u have to decide if that's a good thing to do. There are many people who think a love letter is a turn off but u never want to leave him so I guess it's ok

[Decentguy]

you both should admit to each other that we are insecure but if we promise each other that we won't leave each other no matter what because we love each other very much. saying this to your partner will make him realize that you love him very much and you won't leave him