What is the difference between saying "I love you" and "I´m in love with you" to a person?
Well, I certainly know there is a difference. But I don`t know how to rate this situation:
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Conversation between two people who have been knowing eachother for a long time, really like eachother a lot, treat eachother with a lot of respect, have been flirting with eachother for a long time and who are both very, very attracted to eachother:

Girl: Well, maybe I shouldn`t tell you, but I just have to....I´m in love with you!!!

Guy: Awww, you should see me smiling now. Cause Baby, I love you, too.
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My question: How would you rate this? Does it mean, he only loves her like a sister, good friend, etc.? Or does it mean he feels the same way as she does?

Question

What is the difference between saying "I love you" and "I´m in love with you" to a person?
Well, I certainly know there is a difference. But I don`t know how to rate this situation:
-----------------------------------
Conversation between two people who have been knowing eachother for a long time, really like eachother a lot, treat eachother with a lot of respect, have been flirting with eachother for a long time and who are both very, very attracted to eachother:

Girl: Well, maybe I shouldn`t tell you, but I just have to....I´m in love with you!!!

Guy: Awww, you should see me smiling now. Cause Baby, I love you, too.
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My question: How would you rate this? Does it mean, he only loves her like a sister, good friend, etc.? Or does it mean he feels the same way as she does?

Answer

usually "in love"  is romantic love. 
eachother= each other.

Answer

The response he gave should be interpreted as him feeling the same way, because of the context of the conversation.

"I'm in love with you" always means in a romantic way. "I love you" can also mean that, or it can mean like a sister, etc.

If he had said "I love you, but I am not in love with you,"  then it would mean a sisterly love (etc). But because he knows that she is talking about a romantic love, his response of "I love you," combined with talking about smiling to hear it, means that he is trying to say he feels the same way about her.

Either that, or he is trying to manipulate and mislead her by saying something that makes her think that he feels the same way, but also has a different possible interpretation that he can fall back on later. But probably he is in love with her too :)

Answer

Hm... I would guess that he probably feels the same way about her! There isn't really a difference between saying "I love you" and "I'm in love with you." The best way to tell what someone means (i.e. if they love you as a friend, as a sibling, or actually romantically) is by their tone and the situation.

Answer

Perhaps the first is more emphatic.

Answer

Die zwei Begriffe haben die gleiche Bedeutung.

Verbesserungen zu deinem Text:

--
Fehler = Conversation between two people who have been knowing each other.
Richtig = A conversation between two people who have known each other...
--
Fehler = eachother
Richtig = each other
--

Sonst ist der Text super. :)