[header] How to steal a girl from her boyfriend [title] Build trust. [step] To do this, spend time with her when you can. The idea is to treat her as any other female friend. 
Listen to her problems, try to get to know her better, and spend time doing friendly activities such as going out to eat and watching movies. [substeps] Don't rush to gain her as a girlfriend or else she'll view you as intrusive and only using her as tool for your own enjoyment.