There’s only one answer to this.
You end it with an HEA. Happy Ever After.
All readers want from a Romance novel is an HEA. Don’t overthink this. I include myself as a reader: I want a perfect ending, not something bittersweet or downright sour.
Back in the 1990s there was a series of teen romance novels called Sweet Dreams. The very first one was titled “P.S. I Love You”. “PS” stood for “Paul Strobe” who carks it somewhere before the ending so it ends miserably. I hated it as a teenager, I felt cheated, and I hate the memory of it now.
In another book I read (a student-teacher romance) the she decided to have the hero test positive for the fatal, incurable, untreatable genetic disease Huntingdons after having the fear of it like an axe dangling over his head throughout the plot.
How lovely! The couple has their HEA – for about ten years – whereupon the symptoms are going to start and he’s going to end up a vegetable and then dead.
Life is too damn short and tragedy-filled for grief-wanking. I want to ESCAPE to somewhere perfect and happy for the duration I’m reading a Romance novel. You can make an ending as (unrealistically) saccharine as you like and readers will still love it. Twins. Triplets. An amazing promotion. An inheritance or lottery win that gets them their dream house.
You’re writing Romance, remember. Not gritty literary fiction.
Wrap it all up in a huge glittery bow and have done with it. Your readers will not thank you for a “bittersweet” ending – it’s like trampling on them.