I think we need to deal with some semantics before answering this question. First the “truly” is associated with a romantic notion of “true love” which is more about an ideal and fairy tales than reality.
Next there is the “in love” vs “love”. I think this is a silly distinction but I’ll never forget one of my first experiences with unrequited love in which I told the girl I was “in love” with her, and she corrected me, explaining that being “in love” meant that the feelings were reciprocated. That explanation did not feel good to put it mildly. I don’t know if I buy the distinction, but for simplicity’s sake let’s just call it “love”.
Love is a feeling. It’s not a rational decision. There’s nothing logical about it. If you are lucky, and have grown up with healthy models of relationships, and have internalized the healthy example of loving caretakers, your love for someone will align with many rational and logical choices, meaning the person you love will be a good fit for a healthy, loving and reciprocal relationship.
However, that’s not always the case, and feelings are not based on reason. Many people love those who hurt them or who otherwise unkind or uncaring towards them. I certainly have.
In fact, you can love someone and not even like them, because liking someone is more connected with your rational side. This is very confusing, but can sadly result in us loving someone who not only does not love us back, but may also cause us regular pain through various forms of abuse or neglect.
One of the most important lessons anyone can learn in life is that if someone doesn’t return your feelings, they are not a good match for you. It’s unfortunately a lesson that some people never learn.