He said i was the one..but?

We've known each other for 5 months and we talk everyday for hours upon hours. We are first and foremost best friends. We just clicked and i've never felt so comfortable with anyone in my life, nor have i given someone my heart or trust. I've never been with someone but with him, im just giving in. He respects me and its all about what i want. I love him. We're both in our early 20's and we laugh and joke all the time, We can talk through anything. He's had one gf and im not experienced. I ask him about and he just answers each question then we move onto another topic. Its great and we believe communication is the key to everything. We know that we have feelings for each other but we havent become a couple, he's abroad and i dont want to rush things. We agreed on best friends but we still say those three words sometimes. He's said that even though its been 5 months, he thinks im the one. Id love it but it has only been 5 months and we havent even dated. Do you think its possible to say this in our situation? What do you think? If anyone is in a long relationship, when did you know he or she was the one for you?