Dating outside of my culture update

I recently got ghosted by a guy who was taiwanese, and posted advice for it. Turns out the reason i got ghosted was because he has a girlfriend! She dmed me on instagram and i told her everything and I felt so bad for her honestly. I think as women most of us know how it feels to be in her position. How do I know the signs that a guy has a girlfriend? She told me they live together but i only saw one toothbrush, i didnt see any makeup so im just like what did i miss? I also confronted him and got left on read again LOL.