I don't think Yuuji is lacking in confidence. Once he's made his decision, he's willing to make the move for Chise right away. And from what we've read so far, I think he's a pretty "hot stuff" in that school, with good relationships with his senpais and kouhais. He's also a pretty nice guy, willing to respect boundaries, is caring to his friends and the girl he's dating, and not given to sleeping around. A serial monogamist is what they're called. But for whatever reason, he's being extra careful with his next relationship. We've not given any insight as to why. Maybe a terrible breakup or other similarly painful experience immediately preceding the start of the series, but I'm willing to bet he probably has a good reason for it.