First, let me say that I'm impressed by the forum community. About five pages of comments and only one person suggesting he take the money and run.
First of all I'm a portrait photographer and I've got experience...Second I didn't sign any contract with him and he told me that I could post the photos on my website.
Okay, let's take your second point first – you had an oral agreement with the photographer that you could post the photos on your website. So, that was your contract.
There was no agreement that you could sell the photos. Only an agreement that you could post your photos on your website. Anything beyond that, you are obligated to discuss and renegotiate with the photographer. It may not hold up in a court, but it is a contract and you should honor it.
Now, to your first point. Do you, as a portrait photographer, allow other photographers to accompany you when you shoot portraits? If you do, do you allow them to sell their photographs to the clients?
This is clear cut. There is no grey area here. I agree with virtually everyone else who has weighed in. Your first responsibility is to the other photographer. You are trying to rationalize unethical behavior because your ego has been flattered. Your first mistake was even talking to the bride without going through the photographer. That should have never happened.
If you had just told her that you were there with the other photographer and that all pictures would need to be ordered through him, that would have prevented a lot of grief for everyone involved. Now, the situation has been hopelessly confused and, frankly, there is probably little you can do at this point to make amends to the photographer who was kind enough to take you along. Still, you should try.