I don't really have a 2nd favourite team.
There is a few people connected to clubs I like and a few clubs I want to do well(as long as it isn't to the detriment of The Boro)
Peterborough (I used to go watch them occasionally and quite enjoyed it, but didn't get excited or disappointed the same way I do with Boro).
Hartlepool are like our little monkey hanging cousins and I like to see them do well.
Man U as we have had quite a few major links with them over the years with players and managers so look how they are doing from time to time.
I like Ryan Reynolds as an actor so I have been wanting Wrexham to do well (that's more because I like the person affiliated with the club).
I don't particularly like or dislike Liverpool but I really like watching Klopp interviews and press conferences as he seems like a decent bloke(So another one where I am pretty neutral to the club, but like a person affiliated with them).