What do I do?

Why do several guys I chat with online tell me that they're "in love with me" I really don't think you can be in love with someone without meeting them and spending time with them. Of course I start to in part believe what they tell me because I have a low self-esteem and I have acquaintances in real life but no true friends. Would you believe them or are they just infatuated or full of crap? And how do I stop believing them?