When Mary's happiness meant more to me than my own. I did believe that would be the case when I did fall in love, before I found it to be the case. It has remained so for over 43 years now. Even when I filed for divorce it was still true. I was guilty of invalidating her bisexuality and seeing only her very strong lesbian side, and felt she needed to be free to pursue her needs. I was wrong. She never lets me forget that.
A few reasons: When I can acknowledge their flaws are there, but I still love them anyway (obviously this excludes extreme flaws like abuse, though. I was more so referencing that infatuated people tend to build up a 'perfect' picture in their head) When I only want their happiness even if I don't like the outcome. When I can do 'embarrassing stuff' like using the restroom in front of them or walking in front of them with messy hair/unshaved legs because they've become family. When you actually KNOW the person and who they really are. I believe you can love someone without them loving you back (if you've been friends for 10 years) and you can be just infatuated with someone you are officially dating.
I can't say for sure what that feels like, as I have yet to truly experience it. But from what my feelings of infatuation with certain fictional characters, and my imaginary scenarios tell me, it involves a mixture of an inner warmth, an outward tingly feeling, as well as a sense of elation and excitement. The image, the sound, the body language, and the overall aura of that person just cannot leave your mind. No matter where you are, the thought of them does not leave, and you adore every second, even if it distracts you from other things. But since I've only imagined what the perfect guy for me is (which is almost never a perfect picture, just kind of a blurry guess), I suspect that the feeling of true love towards an actual guy would be 10 times what I've imagined the feeling being. And I almost cannot fathom that, lol. But I'm sure it would be amazing.
I thought I had been in love but I don't think I have. When I've read stories with romance it sounds amazing. I just don't think I've ever really made that kind of connection yet.
When I can't stop thinking about them, want to be with them and be comfortable around them. When their flaws don't matter, not counting major things, and I love seeing them happy. Also when I trip over myself and show more emotion in front of them because I love talking to them.
When I can't stop thinking about them, and want to be with them all the time. And I feel amazing around them.