I think it is unfair if you want to be with him ultimately because the guys that you're dating may actually be interested in starting a relationship with you and you're seeing them under false pretences.
On the other hand if you want to move on from him then sure, why not?
It's difficult as he said he cannot be with me as he has problems. I know I shouldn't wait as life is too short but I am worried if he finds out I went on dates he thinks I have moved on - part of me still has hope. I agree it's not fair to give other guys false pretences.