First, step back and stop the battle over his bowel control. You know the old adage "You can lead a horse to water but you can't make him drink". Boy does this apply to kids whose parents are trying everything(and indicating their displeasure and disappointment) to get their kids potty trained. You have to relax about this and let him come to make his own decision on when he wants to use the toilet to defecate. He already has urinary control(which is physically harder to master than bowel control) so that should be praised and celebrated.
Keep a potty chair in sight and tell him he can choose to make his bm's in his training pants or on the potty. Tell him he can tell you when he has to make one or go over to the potty and pull down his pants and do it on his own. The first step is to get him to tell you when he has to make a bm. Where he makes it will be his decision. When you feel he is choosing the potty more than his pants you may want to locate the potty next to the toilet and then give him the options to make it in either place. You might even tell him he could practice on the toilet and make it in the potty for a while.
Stop the battle. Ease the tensions. Praise any progress. Let him be in control of his body and let go of seeing this as a control issue between you and him. Your burdens and his will soon disappear. Good luck.