Lost when it comes to love

I’ve got a situation. So this guy I’m talking to is super sweet and extremely romantic at heart and for what ever reason he seems to like me. A LOT. I think I like him. I enjoy talking to him, but I’m just not sure. I just feel all knotted up, but seeing as this is the first relationship that I haven’t avoided, I’m not sure if it’s a good feeling. I’ve agreed to be his girlfriend, because I can’t see a good reason as to why not. The biggest problem is that he is like a brother to one of my closest friend. I don’t want to hurt him or lose her, but I’m not as quick to fall for people like they are. He already said he loves me. I know it’s just because they are extremely romantic, but I’m just not sure about my feelings. I know he’s a great guy, and I do want to like him like that, I’m just feeling... lost, confused, and rushed? I really don’t know what to do. Please help!