From Longman Dictionary of Contemporary Englishgo steady (with somebody)go steady (with somebody)RELATIONSHIPto have a long regular romantic relationship with someone → steady
Examples from the Corpus
go steady (with somebody)• If you can't, it's as well you're not going steady.• Somehow, the mention of marriage has strained even the sweet pleasure we found in going steady.• Tell her you needed time with the idea of going steady, and you need time with this.• Maybe they don't talk about going steady any more, he thought.• I could really go for him in a big way, but he's going steady with the staff nurse on Rainbow. 