How do men usually act if they are really in love ...

Anna,
Don't be mad at me but your question indicate that you meet with the wrong men and they confuse you.  I can promise you that when you meet the right man you'll walk on safe grounds (and you'll sure know that he really loves you... you will have no doubs and have no questions, like this, to ask). 

The person that you are associating with is in lust.

As to whether or not he is in love is a totally different question. Just in case you wonder if you might not know, although OronD suggests that you will, here is a partial check list-

Does he share your interests?

Is he thoughtful and courteous?

How does he treat your family? your pets?

Does he expresses anger toward you at any time? If so, how does this look?

Have you been together long enough for him to forget  your birthday or other important occasion?

How do the two of you work together on any given project?

Well, for we men, it's pretty much about sex either way. But a man who is in love rather than lust is the man who takes the time and effort to really get to know you as a person. A man that's only thinking about sex doesn't care who YOU are. A man in love does.

I guess this depends on the guy. Anyway with me, I'm not into sending a lot of messages and passing my time complimenting her.

I feel more in love, not when I'm not with my girlfriend but when I'm actually with her. It's just this feeling of being totally in the moment, happy and fulfill. Being entirely attracted to her on emotional and physical level.

I wouldn't actually consider, you should tell if a guy loves you or not, just by the amount of messages he sends, or he compliments you all the time and does everything for you. It has nothing to do with that, I disagree many times with my girlfriend, and like to do stuff my own way and has nothing to do with not liking her. It's just because I like myself more lol :)

However, for me it's more about the connection I have with her when we are together. I also care for her, not that I think about it but my girl tells me all the time that she feel protected, when she is with me. So it's pretty much, a guy being there to protect you no matter what.

When they meet you, they feel pleasant. They will care you, respect you. I once saw an American guy who loves his Russian wife. They met on a dating site CharmingDate.com. Though sometimes they have some difficulty in communication,  they have fun staying together. Sometimes they just give some caring words; sometimes they just stay silent. But it is happiness.