The former Halifax and Hyde boss stepped away from his role as manager of the NPL Premier side yesterday, but he has been quick to praise the club for their support during his time in the hot seat.
He said: "I have stepped away from my role as manager and I am not going to be a manager anywhere else.
"I want to put on record all the thanks that I have for everyone connected to the club, the board, the supporters, the players.
"I have really enjoyed my year and a half with the club, I have met some absolutely fantastic people."
The 41-year-old, who joined at the end of 2019, was in charge for 29 competitive games during his time as Boro boss, winning 14 of them, believes his successor will be walking into a great job.
He added: "The person to step into the role, what a great job they will have, working with great supporters and a fantastic board. The next manager, whoever that may be I will happily go everything with them.
"It is a big job, there's a big demand in that. You can never have it all your own way there will always be challenges, but the key is to build relationships within and connect yourselves with the supporters.
"In life everything is about people, you need to build strong relationships, and that is what I have tried to do with people on the pitch and off the pitch. The board saw the vision I was trying to implement, and the supporters saw that too. It has been a fantastic journey and I wish the club the very best.
"It was not an easy decision, it was a very tough decision."
Concerning a return to the club in the future in some role, Kelly did not rule this out but was keen to re-iterate he is stepping away from management.
He said: "You can never say never but management at this time is the furthest thing from my mind.
"The opportunity has come to step away from management and focus on other things. I would like to hope one day I could return in some capacity."
In his final message to the fans, Kelly said: "I would like to say thank you to every single one of them.
"From day one they have made me feel welcome and backed me from day one. Whoever comes in is getting one heck of a club to manager, one heck of a support to work with and one heck of a board to play with and players-wise absolutely amazing.
"I will never forget the support they gave me."