I can really imagine what you're feeling - especially thinking about you imagining what your wedding day might look like, and of course it includes your entire family and friends! But now is not the time to be committing yourself to anything that you expect to last your entire life. You are clearly in turmoil. I suspect most people have had thoughts like yours of "I wish I could just die" because life seems too pointless or too fraught with trouble. I hope for you that's all it is, and it doesn't sound like you're suicidal (there's a BIG difference between wishing for death and contemplating doing something about it) but that's definitely an indicator that your life isn't going as you'd hope - when things are bad is not the time to be getting married. Get married when you're happy because you want to stay happy, don't get married when things are rough, thinking that it will somehow fix it. It won't, this I promise you.
Another thing to keep in mind here is that people are really good at seeing how they might lose things unexpectedly (or in the case of family relations while leaving the cult, it may well be expected) but we're not so good at envisioning how we might gain new/better replacements. You can imagine losing your family, but can you imagine meeting new friends that you feel so close to that they feel just like family? Can you imagine having those feelings of love and closeness with people that you currently have not met? It's difficult to imagine for most people, but it's 100% possible and if you find yourself in need of new family and you do a little looking, you will find that. If you wait to have a wedding until things are more settled in your life, you will not have a wedding with no family present - you will have a wedding with your true family present. Would you rather look back at wedding photos full of people that you no longer know because they disowned you when you left the cult, or would you want to look back at photos with people that love you for who you are and not what you profess to believe? People that will stick by you through anything, not drop you at the word of some janitor in a suit?
I'll also tell you that once you leave the cult your life will change in the most unimaginably wonderful ways. You will finally begin to figure out who you truly are. I'm sure you've started on that project, but until you've been able to put the cult behind you (i.e. no longer going to meetings, no longer spending all your waking hours researching, no longer boiling over with anger at the mention of the blood policy or child molestation, etc.) you have only begun to crack the surface. Once you get beyond the gates of the cult and start exploring the real, glorious wold beyond - that's when the real work starts. You don't truly know who you are at this point - is this really time to be thinking about marriage?
Ok, hopefully at this point I've got you at least considering that maybe in the long run waiting to get married is best...and that's before I've started talking about the boy to whom you're thinking of becoming married. First, you need to make sure you've made yourself clear to him. It's easy to say something and know what it means so perfectly (having all the context of your internal feelings and emotions) but for its meaning to be completely missed by anyone who's heard it. Focus on facts, not judgments ("When I talk about the cult you just nod along without contributing to the conversation, or change the subject" NOT "You're so cold and unemotional!") and then tell him how it makes you feel, and why ("It makes me feel alone because I need to know that you understand my pain" for example). This is sort of the classic "therapy talk" for couples (and any relationships, really) and it is so for a reason - it can make a huge difference. It might take a little time, so don't get frustrated if he doesn't get it right away - ask him to repeat back in his own words what he heard. Once you think he understands how you feel, try making a request, focus on something he can do RIGHT THEN. Ask him, for example, to share his feelings on the cult - maybe it's not that he has none, maybe the cult's repression has made it difficult to open up. Or you might request that he just listen to you as you tell him how difficult things have been for you, while repeating back what he's hearing you say (so-called reflective listening) this can go a long way towards establishing empathy in him and it will likely help you feel that he has listened and not just coldly nodded along. You are clearly in tremendous pain and the fact that you're on an internet forum looking for compassion from strangers, having felt none from him, tells me that one of two things is true. Either he doesn't truly know how you're feeling (maybe you've explained things in a way that he doesn't understand, or maybe he hasn't listened) or he doesn't care. Do you know which one it is? If you're thinking of marrying him, it seems like a very important question to know the answer to with certainty.
In summary - you need to banish the thought of a wedding until you've got your life on track. Get married when you're unhappy with your life and you'll walk into a marriage that leaves you unhappy with your life. Next, you need to talk to your boyfriend and work on actual communication. It would probably benefit you to do some reading on how to communicate effectively in a relationship - this is not a cult-specific problem you're facing, it's all too typical, and as such there are going to be tons of resources online to help you.