...to commit suicide by potion?

I'm thinking about a love story roleplay between the PC and a follower - deleting all saves somewhere around level 30 - and upon the next death of the follower, the character commits suicide by potion thus terminating the game.

it would have to be a potion with some strong damage health negative effects.

Romeo and Juliet?
anyways i think that the only poison capable of killing a character with one dose (without exploits) is one made from Jarrin root and crimson nirnroot / river betty. Since jarrin root is unique you'll also need the Sinderion's Serendipity perk if you want a chance to get more than one poison.

(make sure the potion you're making has a positive effect so you can actually drink it)