Sorry to hear about the tumour, Kezzer, and I sincerely hope everything works out for you. As for faith, if it's a comfort and a help, then it's a comfort and a help, regardless of whether it's 'true' or not, and I'm a great believer in "what works, works".
And I might be a lot of things, but I'm certainly not arrogant enough to be convinced I'm right and you're wrong, and that's the end of it. It's just the view I've developed into over a considerable period. I'm not even arrogant enough to not concede that something could happen to change my perspective.
And yet another perspective is ... if you're wrong and I'm right, you've lost nothing. If you're right, and I'm wrong, I'm probably in deep poop. So, potentially and rationally, belief is a lot smarter than scepticism, right or wrong.
Please also take this without offence. If you've lost very good friends over this, despite your situation, then I would question whether they were as good friends as you think they were because, in my opinion, that sucks. True friends would be supporting you in a time of need and pressure, regardless of whether they agree with your Christianity or not. It's dangerous making snap judgements from the outside, but falling out with you over that, at this time, suggests they not only weren't good friends, but weren't very nice people either.