Why do men lie?

I just got out of a relationship, currently mingling with other men and I recently met this guy off a dating site. The pictures he posted was 16 weeks ago and he tells me he just broke up with his girlfriend less than a month ago because she cheated on him. So he'd still have a dating profile while he was in a relationship with her? He also claimed I'm the first person he met from online and he's never had an online dating account before. I don't know what to believe and the fact that I caught him somewhat in a lie makes him seem like a shitty person and gave me a bad impression of him. I don't want to assume but this is what is constantly crossing my mind :( sucks because I really liked him and we clicked so fast.