If I could go back in time and speak to my more-naive self, something so important I would tell myself is: A person's actions and words need to line up, AND, you can't force someone else to feel the same way as I do about them.
Unrequited love, hand-in-hand with rejection, has got to be one of the most painful human emotional experiences next to grief over the death of a loved one. Because once you finally accept within yourself that the human object of your love doesn't feel the same way in return, it can result in very deeply damaging emotions of grief and despair. I know because I've been there, I've unfortunately had the experience of it, rough and in the raw. And no amount of time or therapy can change the memories of it. They are what they are, and are written in the sands of time, and Akashic Records of Heaven.
Loving the "wrong person" can deplete the life force out of you to the point where you feel next to death, and maybe even feel like you want to die. It's THAT exhausting and awful. Whatever the deep spiritual lesson the experience may contain, it sucks. Maybe it's as simple as: if someone doesn't reciprocate love and actions, cut loose and move on asap. Otherwise, you could end up a depleted washed-up soul-vagabond. Giving to someone who's basically like a black-hole. Sucking away your energy, taking all you give, and not valuing or returning it. Basically taking you, your love, and efforts for granted.