Here are my answers on your questions (definitely biased answers HAHA)
1. There's a lot of answers on this one actually but mine would be, when you can't get him/her out of your mind, you get a little bit jealous when she/he talks to an opposite gender and that you are somehow or somewhat imagining your future already with him/her..
2. I'm not sure about my answer on this one, cause i don't quite understand your question.. Im'ma assume that you're askin' about knowing if you just love the idea, only the idea itself. My answer on that one would be an example, for example you encountered some bad situation with her/him and she/he shows a not so pretty response or action, causing you to lose a little bit of interest to her or to him. That would be a perfect example of you liking only the idea of being together with him/her and not really fully committing to a relationship.
3. My answer on this one would be exactly the same as my answer on number 2.
4. This one's actually pretty easy. When you are being pampered or showered with affection or love and you are lovin' it, while at the same time don't wanna put same effort unto her/him.. That is definitely a sign of you just wanted the feeling of being in love and not the other way around.
5. I dunno about this one HAHA.. Maybe after you've had some s3xual intercourse with that person and you lost interest to her/him, that would be a sign that you only want to do that specific thing with her/him.. While if you still haven't lost that interest after a steamy night, that's love right there (still not pretty sure on this one though HAHA).
hanggang dyan na lang po ang aking lutang english answers HAHA.. Hope it helps