What to do... League situation

I have been commishing a league for the last three seasons and this is the first real trade issue I have had. I am not one of those "unfair" trade commissioners. We have never had a trade vetoed in my league. The league is 12 guys, most of us are IRL friends, and 4-5 others are friends of friends.

The guy I started the league with, we will call "D". D's Cousin is also in this league. Earlier this season D's cousin wanted Peyton Manning really bad. He traded D DeMaryius Thomas (who was off a 5 pt week), Ray Rice (Q with hip flexor), and Jimmy Graham (putting up sick numbers) for Peyton Manning. This was a very one sided trade, but Manning looked to be on a record setting pace and 2 of the three players were struggling at the time.No one in the league cared much about the trade, so it went through without a hitch.

Tonight, I had a FF convo with "D" who is a good friend of mine. He told me that one of his friends "J" had told him a couple nights ago, that if he paid half of his league dues ($25) he'd trade him anyone on his team. D told me that he told "J" that he wouldn't do that, and it wasn't ethical.

D also told me tonight that J told him he was interested in moving Marshawn Lynch. D sent a lowball offer of CJ Spiller and Joseph Randle to J for Marshawn Lynch. He claims it was a starting point and he expected a counter offer. Well, I just got a call from D telling me that J had accepted the trade. I was pissed.

Am I wrong for telling him off, paying my dues and finding another league next year? Should I be a dick commish and just veto the trade, even though he told me it wasn't collusion (i do trust him for the most part). I am having a hard time believe this guy could think this was a good trade for his team. How would you guys handle this situation?