If you lived forever you could LIVE for what you believed in.  It's basically like a martyr but without death.

I would prefer to die doing some heroic act in saving another human. Why would I want to give up my life for delusion?

Living forever is a long time. I will die, as all will, and my constituent atoms will be recyled into the universe.

Tell him that you two are better off just friends. I can't tell you exactly how to end the relationship whether or not it's over text or in person but my only advice is don't leave him hanging

Do it in private, away from other people. You never know how he's going to react, the tears might flow and you don't want him to be embarrassed.