Hi,
I've created an object and I added a subset and made the textures blend.
But ingame the object faces seem to come and dissapear. I included a picture from different sides, any ideas?

Unfortunately the game has something wrong with the way it draws "blend" mode transparency. If you want some parts of your object completely cut out, ie transparent, you should be able to set blend mode to "none" and use alpha test enabled instead for your alpha channel. If you really need the semi-transparency, try to make the subset so there will never be another face of that same subset behind the face you want in the foreground and also facing the camera. Eg a cube is ok, a torus is not.

is there a tutorial for this?

I wouldn't know which one specifically deals with it, but if you browse thought the object meshing tutorials one of them should help. Otherwise a search on "bleed" or "bleeding" may bring something up, as that is what it tends to be referred to as.