The feds set Opie up to make it look like he was betraying SAMCRO. Clay fell for the set-up and ordered Tigg to kill Opie. Donna was in Opies truck and Tigg killed her by mistake thinking she was Opie. Jax and Opie's dad suspect/know that Clay is responsible for Donna's death. That is the cause of the tension between Jax and Clay.

so could someone tell me why piney would let oppie follow clay and shun jax out???? The old man knows what needs to be done, but yet he lets his son go the wrong way, and i could very well be oppies downfall, he is too brave or stupid now.

I think Piney is trying to protect the club from Opie's rage and trying to protect Opie. All Opie has left is the club, if he finds out the club killed his wife I think he would go crazy.