Being a Marxist isn't about belief, it's about analysis. If you're hoping to read something to gain some sense of certainty on the order of the world you're looking in the wrong place. If you want to figure out how the world works, then you can, but it's a process of discovery. Read capital. If you've been a Marxist for that long you can begin it, or just read more theory in general. Try to start forming your own analysis and ideas. Idk. I think we need everyone to be looking at the material conditions and trying to figure out what is to be done, not just reading old texts and repeating old strategies.