Helping each other

[magicalthings]

I am looking for a story I can't remember but I think I read it on Fanfiction but can't be sure. In it I think Harry needs Severus to brew him a potion and Severus says yes only if Harry does something for him, needing this potion Harry agrees saying he will do anything. Severus needs to marry for some reason and Harry says yes and they get married but Harry thinks they can marry to get Severus what he needs and then divorce only to find out after they are married that once married you can not divorce.(I think the potion Harry needs is because he can't come or get hard but not sure) anyone have any ideas what this is please?
Found! Link in Comments!