hello ^^...in Japanese there are 3 ways say "I love you" 大好き（daisuki) to friends and to the person you like. 愛してる（ashiteru) when you have a relationship would be with that special someone. 恋してる（koishiteru) the person with whom you want to spend the rest of your life. It's one of the things I admire about them, do not allow the "I love you" lose its meaning. ^^ well I hope you serve something .. see you :D

I think it's very good and interesting questions. First of all, you should know that we're really shy people, so you barely express our feelings, especially the strong ones. Guys tend not to even now. So we barely say "I love you" to anyone. We don't say "I love you" to even our parents. I know it sounds terrible, but that's our culture lol. I think the only situation we say those type of things is propose or those kind of situations. Then let me answer your questions. (1) 愛しています (2) 大好きです (3) 大切に思っています　(ambiguous expression) (4) ずっと一緒にいたいです　(ambiguous expression) Since it's very hard for us to show our emotions, we say these in ambiguous ways. And we have a lot of ways to say "I love you", because it is way more comfortable and convenient. I hope it helps :)

Hello dear, I look you are from Vietnam too. So glad when you want to learn the Japanese. It is my University. To say " I love you ". You can use this Grammar structure : " 私は君( you- the girl)/あなた( you)を愛している” And " I like you " is ”私は好きです” in Japanese. Anyway, if you want to enjoy in the Japanese, you can contact me to discuss together. Because I also want to practice my English, and so well if you are Vietnamese too. Good luck and see you!