I thought about this for a long time. I don't think in terms of "do I like this person?" Instead, my behavior is more or less instinctive. I can tell how someone feels about me, and I react according to that. If I get the impression that someone likes me, it's easier to just be nice to them.
In other words, my attitude towards a person depends on their attitude towards me. Ofc, this isn't true always. Sometimes I dislike people who like me, but it never happens the other way around.
Give them some more