I think that you can say you love someone enough to make them your soul mate if you always put their happiness above yours. If you want to be with them even when they annoy you, if they make you better, and if you make them better. I think the concept as the world uses it has to do with reincarnation, though, so you might want to be careful who you say it to. I think I've found my "soul mate" because I want to make him happy all the time and I want to be a better person for him. He understands me like no one else can and I feel more comfortable with him than anyone. I think that's what's important.