How to break it off with Japanese boyfriend?

He's a westernized Japanese guy and he's wonderful. He's done absolutely nothing wrong. But after we'd sort of confessed our liking of each other today...I can't help but feel so much regret. I do care for this guy and we've had a long conversation about how long we've liked each other, uni life, skyping etc (it's a long term relationship). We've known each other for a few months but we quickly figured out our feelings, now I just feel childish for making a decision to be his girlfriend so soon.

The truth is, I don't seem to have much of an emotional connection with him. There is another guy, Japanese, whom I have actually cried over twice because I missed him. We're still friends and he's strongly hinted he likes me back. He's not westernized he's a traditional Japanese but we can communicate just fine. I feel like I'm betraying the Traditional because the Westernized has straight forward told me he loved me. I thought I felt the exact same way today and yesterday too. But ever since we stopped talking for the day I just feel...like it's not right. The reason I find it so hard to break it off simply is because at first when Westernized asked me to be his girlfriend, I said there are so many issues we'd have to deal with so it's better to wait, then I said actually I've thought it through and I've decided I'm ok with this. Now if I break it off I'll be losing a great friend and also I'll seem so childish after changing my mind again. It's a ridiculous reason not to break it off because if I don't it's a recipe for disaster and it's selfish of me. So how can I break it off, how should I handle this? Advice much appreciated!