I like to use Anki with some shared card decks: https://ankiweb.net/shared/decks?search=german
The learning pattern that Anki has configured by default suites me quite well and the app and the card deck is highly customizable.
Mind you, this is mostly only for learning vocabulary, not for learning grammer.
I can understand your perspective, but I want to offer an alternative view, maybe less bound to societal preconceptions. I married my partner for many reasons, financial, wanting to raise a child together, wanting to share my life with them… But staying married for the rest of our lives is a crazy concept for us. The marriage has its purposes, but we both know that life can change and that we could decide that we had a good time, and that now the time has come to move on. A marriage is less romanticised for us, it has practical reasons. I guess being polyamorous helps with defining new relationship ideas on many levels ;)