In writing a backward-trending narrative, is it wise to write it in past tense?

I am writing a story in narrative-form without dialogue, 1st person. The beginning is the end, and I need to move backwards from here on out—but I like the “nowness” and effect of the present tense as opposed to past tense. But how do I tie it back without using past tense? Here is my first paragraph (unedited, for now):

A melancholy and determined Jenny opens her door to leave and I know now that this is how it ends for me, for us. And in the midst of my shock and grief and pain, Jenny closes the door, and I am amazed by the education I receive—the knife, along with my skin and guts and other innards that Jenny had decided not to consume, lay all around what is left of my half-mangled core.
———-
From here, I need to work backwards. Should I say: “i think about….when….” but then that requires past tense.

Or if I just keep it in present tense, it might lose the reader. Like if I continue and write:

Jenny and soandso fight and make love, etc….the reader would be like – wait? when is this happening. But might that effect work well at the end….?

Sorry for the confusion – just hoping for some guidance.

Thanks Fluthericians!