Should I pull out from the interview?

Hi,
I am currently applying for the position of second in my department. I have an interview this Friday and I honestly do not know if I want it.
The current DOL English does not believe in me, every time I meet with him to discuss my goal of being a mentor for trainees, he puts me down and gives it to other teachers.
I currently oversee homework across the school and have been struggling with the SLT lead on this. I receive A LOT of emails from this person and have sent these to my DOL to support to which I have received "What do you want me to do with this information?" I do not get paid for this position, the Maths homework lead does.
I just feel really disheartened by the school, I feel like the place is a dead end and I will never progress here. Yes I have an interview and there are two roles but 1 is already pretty much assigned to a senior member of staff. She deserves it. The other? Me and 2 others who get on with the DOL are fighting over.
I just have no fight left in me. I am so deflated and really need some support.