I(20f) fucking up with my(20f) friends bf(20f), how do I get out of this the least messy way possible?

So here is the situation. Our mutual friend Sarah invited me and Steven to her house to hang out. I agreed not knowing it was his birthday. She kept it a secret because that was what he wanted. Her and Steven have been friends for 6 years. I just met Sarah in College but me and him have been friends for 4 years. He used to be a chubby kid and he’s always had a thing for me. I’ve always been flattered by his love but I’ve never been attracted to him. He’s lost a lot of weight and his feelings have not changed. He’s always making subtle moves on me. He had a gf a few years ago and I thought his feelings were gone but he still has them. So at Sarah’s we are hanging out. She has to go pick up food so she leaves me and him alone together. He’s being flirty and making jokes about us hooking up and stuff. I was joking around with him but I was also kind of just humoring him. I was not trying to lead him but we were both flirting. Then Sarah comes back and we stop but he’s still being flirty with me. So the night ends and we are all hanging out again on campus. This time his gf is around. He tells her about us hanging out and I can tell she’s annoyed. She asks me directly if I knew it was his birthday. I tell her I didn’t. She then asks if I was flirting with him. I answered I wasn’t but I’m starting to wonder if I was. She says she know I was because he told her. He admitted to her that he flirting with me on the car ride home. I was like ok so she know he flirted so she should know it was mutual. She then asked if I would date him if he was single. I was just humoring her at this point and said of course. She then said ok so if he was single you would date him and I’m like yes. She then said that they are now broken up and that she’s going to go tell our friends they broke up. I was kind of shocked. I didn’t think she was actually going to break up. I was just answering her questions. I then go to text him and he’s telling me how I broke them up. I was like what the fuck. He admitted to telling her he was going to leave her for me. He said how he has been in love with me for years and how he could never love her like he could me. I was honestly flattered so I was like ok we should date. Now it’s been 3 days and I feel really guilty. I don’t want to date him at all. I feel like I broke them up. She won’t even talk to me. How do I just break up without it being messy? I don’t want her to think I’m some homewrecker. I don’t know what to do. I feel like I ruined everything.<br><br>TLDR: I was just hanging out with my friend. She had her bf over with me. We were flirting and the next thing I know they broke up and now he’s telling me how much he loves me.