Utsuo has answered very well and I'd like to add a bit more. When our children are small, we often say だいすき but after being a bit older, we don't express our love that much. So, sometimes it seems that "Japanese people are very cold". Besids, we never say to our friend, "love you, bye!", "love you bro" and to give "hug" each other is very rare. If you do so to your male Japanese friends, they might think you love them romantically and their girlfriends wouldn't feel fine. Even with our children (who aren't small) we generally give them hug nor kiss though it depends on the person and family. I think this culture is because of our history that hiding our emotion/love was good. Watching the movies with subtitles, sometimes we find the difference in our expressing in each language. For example, we don't call our children "sweetheart", so on the subtitle, it's often showed "(name)-chan / kun". When I contact with my foreign friends in their language, I say/write "love you!" and "bis hug" but when we talk/write in Japanese, we don't do that. It's interesting but a bit weird in my opinion. I hope this was helpful.

Actually, "aishiteiru" doesn't mean just "I love you" with a romantic connotation, it also can mean deep care and affection, like for family, but saying this to a friend may sound too strong. "Koishiteiru" has a more romantic meaning, but less deeper than "aishiteiru, of course. But today's japanese people don't use "aishiteiru" so much, it is rare, except for dramas or songs maybe, so "suki" or "daisuki" is more often used between couples, friends and even among family. As for "I love you bro" after he/she did something really nice for you, I don't think saying "I love" sounds good, instead you could say just "sugoku tasukatta" that means "It was a great help".