Dont confront her about it right away and straight forward without warning.
Next time you're hanging out just ask her how things with Steven are.
She'll either say good, or not so good.
If she says not so good, ask her what the problem is, dont let fear of her liking you stop you from being a good friend.
If she says good, you say "good" then ask sarcasticly "so how far have you gone? *raise eyebrows up and down in a sarcastic manner so that it seems like your asking just to bug her in a friendly way* She'll most likely tell you if you're alone, then you just come out and say "why would you go so far with him when you've only been dating for _____ days/weeks and you never hang out with eachother?
I cant predict what will happen next so just go with your instinct.
I went through the same problem. Almost the same exact problem and i did exactly what i said you should do, and it worked out perfectly, she stayed with her boyfriend, they didnt go farther then kissing/making out for about a month or 2 and then gradually took their relationship to higher levels.
good luck man.
