Shawn Mendes is talking about how he has had his heart broken so many times in the past, and it happened again with this girl. When he says "I thought that i've been hurt before but no ones ever left me quite this sore," He means that he thought that passed breakups have been bad, but this one was the worst of all. When he says, " Aching begging you to come help and now that I'm without your kisses I'll be needing stitches," He means that he keeps begging her to come back to him, but no matter how many times he tries, she always turns him down. He now doesn't have her so he feels like he needs stiches to heal him. Eventually everyone finds the right person. I actually relate to this song, because no matter how many times I like someone and try to go out with them they always brake up woth me in the end. I do love this song though because it relates to my life.