I. A verbal agreement is a contract... It's just darned hard to prove. If there were a witness or two to your agreement to shoot on his behalf as a 2nd shooter, then he might be able to prove it in court, if it ever comes to that.
2. You have just admitted to your verbal agreements here on the Internet, in a public forum.
3. Shooting with his camera does complicate things. When he provides the tools for you to do the work, it implies even more stongly his ownership of the copyright on the work you do, while in his hire.
4. It is not uncommon in wedding photographer for the copyright of work done by a 2nd shooter to pass to the hiring photographer. It's understandable in some respects that they might need it, perhaps to provide prints or files to customers months or years later. Simple transfer of copyright is the "cleanest" way to do this. The 2nd shooter can be given perpertual, irrevocable license to portfolio usage of the images, so long as it in no way intrudes upon or impedes the primary shooter's relationship with their client.
5. You do not need a signed model release to show images in a portfolio context. That's specifically excluded from requiring a release, under the law is treated as "editorial" usage. Just don't use them in any other "commercial" way without a signed model release. If the portfolio is online, and you are ever contacted by the persons depicted in the images, they object to your displaying them online, simply take the images in question down. No big deal.
6. This should be a big object lesson for you.... Always get it in writing! Even with friends - maybe even more important with friends, in fact - I sign a second shooter agreement... Always! All the terms and conditions must be spelled out and understood by all parties. The best way to do that is in writing, to prevent problems later. No matter which side of the agreement I'm on at the time, I won't do a 2nd shooter arrangement without everything in writing and signed in advance. It was very unprofessional of the primary photographer to hire you without a signed agreement. It wasn't your responsibility to bring the agreement to the table for his signature.