Who did he trust that he was told not to?
I think you're referring to Robb Stark..
Robb was fukked as he had his mom undermining his leadership..
Robb was too naive too..Ned wouldn't have married a foreign nurse..prolly wouldn't even have slept with her but Ned was smart enough to know an alliance with the Freys was worth more than some honor of a smallfolk bish.
1. WILDLINGS. THEY WERE ABOUT TO SERVE HIM UP WHEN STANNIS ROLLED THROUGH.
2. DRAGON BISH. SHE BASICALLY HAD THAT CAT AS A PRISONER. HE ONLY GOT TO LEAVE BECAUSE SHE WANTED THE D.
3. NOW HE'S TRUSTING CERSEI TO HOLD HER PART OF THE BARGAIN.