Can't remember if they did say his parents split up in the anime, but I always had the feeling. If they didn't say it, it was very much implied. Seiya did say that his parents fought over him and stuff, which wouldn't quite make sense if they were still together. Child stars getting separated from their greedy parents is also apparently not uncommon in the industry at all, which is pretty fucked up.
This last part is important, because Seiya could have easily come off as entitled or needlessly edgy in a lesser story. Nice to see Gatou unapologetically go for "fuck his parents" in a way that flows well and reinforces Seiya's commitment to the park and his duties, as well as illustrating how much he has come to value his pack of weirdos. Forget manga, in most other stories in general, the lesson would have probably been something like "family is forever~ Forgive and forget~" with loads of cheesy drama, but I like how both here and in the anime the parent trap is basically run over without looking back.