Disregarding the speculations if they were just together for business or not.
Like normal relationships, being together as long as they were together for, either you get married or you break up like Taew and her Ex of many years. I feel like you both have to have no intentions at all for marriage and kids so you can live the life freely without those things to "tie" you down, like Anne T and her boyfriend of many many years who just date, or both be wanting marriage within the same time frame. Maybe it takes really being apart emotionally and physically to really be honest without yourself if you imagine your partner being in the future you picture for yourself and perhaps him being away in Australia for that long made them both realize they couldn't see one another being in that future together. While for some like Prang and her now fiance, who I think did break up for a little, to realize that they couldn't be without each other and chose to marry.
Lol Bella might just stay single and then end up with a high-so. Being together for so long with a equally big name actor of your league basically, I don't she would date another actor again. But if she really is single, at least she can play up her koojin pairings now and be flirty.