They do divorce, then there's a failed rebellion that happens afterwards. Harsen is part of the rebelling faction, while Ercella is on the side of the reigning royal family (her nephew is the Crown Prince, the one that her sister died giving birth to).
So, a lot of things happen in between, but they do still get together in the end. It's not all flowers and butterflies. IIRC, in order for them to be together, they left the current empire and moved to Ercella's mom's country of origin. As it turns out, Ercella's mom is royalty in her country of origin, so Ercella is also accorded royal status. They had to move because Harsen is a criminal in the empire by virtue of his participation in the failed rebellion.
Ercella does not forgive Harsen so easily, but at the same time she recognizes that she wants to be with him, so they make it work -- so the move to another country. Harsen assumes a new identity, I guess. Their son Vincente joins them in their new country at some point. She eventually gets pregnant for the second time. She also proposes marriage to Harsen. But all of these good stuff happen after some time has passed (remember, she doesn't forgive him right off the bat). Cmiiw, they haven't remarried each other at the conclusion of the novel.
Personally, it isn't the ending that I want, however, the way she accepts and deals with her conflicting feelings of not wanting to forgive Harsen and at the same time wanting to be with him, makes me like her. I mean, I don't think I'm the only one who has been in a position where I've felt very conflicted about a person or a situation. For example, I admire my over-accomplished boss, but I also hate her because she's a slave-driver and a micro-manager. Also, in a way, it gives us another perspective on forgiveness and somehow simply accepting that people are flawed (we all are) and how do we continue on living with that unchangeable fact. Or, maybe this is just me wanting to see the best out of this novel/manhua.