forge has updated to minecraft 1.8 and i was hoping that blood magic would also update to the new forge version.

1.8 is a big update for mods, and a lot of backend work needs to be done for the mods to even function. Not to mention the fact that the 1.8 forge builds are VERY early, and still need a lot of work done. Add that to the fact that all the changes would almost force an author to keep two copies of the code, needing to fix every bug and add every feature twice... For now, many authors are waiting on 1.8 to be a bit more stable and complete before moving.

Even a small mod has more than 3000 errors. How many errors will Blood magic have?

Way was trying it out and had a couple thousand errors. Many of them are because of normal refactoring of events and the like, but some are due to the new rendering methods. Some things in BM just aren't feasible at the current state Forge is in. Won't be for quite some time until BM (and many other mods) even seriously think about moving to 1.8.