"Suddenly, boom, he starts chatting to an 18 year old on the internet. This lines up perfectly with the enormous volume of pornography that he views. Sure, he'll have to talk a lot of rubbish about making a connection and how much he feels like he's known you for so long etc - but everything in his mind is going to be concentrated on what an absolute hero he is for getting with an 18 year old."
I think that when a 30 year old man, starts to date a teenager, his motives might be that he wants problem free pregnancies from a girl in her fertile years. He also wants a girl who is sexually inexperienced, so that his own sexual performance in bed, cannot be compared to her previous partners. He also has a "Madonna and *****" complex, (maybe from his religious background) so that a girl who isn't a virgin is (in his mind) a *****. He also wants to control the girl, refuse to allow her to work, or gain qualifications, so that she is 100% dependent on him for money. That way she cannot leave him or risk making him angry.
So in this case, wtih an 18 year old, who has been groomed on the net, fooled into thinking he is a future partner/husband, it is obvious what is going to happen. She will be used for sex for a while, and then she'll find he's cheating on his wife/partner. She will have her heart broken and yet, that is so much better than being ensnared by this type of man.
Better to get "wised up" on how life is, and then learn to live it on your own terms, than to get romanced by a creep and put into a prison by him.
Because by the time she's 45 and he's 58, most of her life will have been sacrificed to him, and inevitably she will find a way to break free, and life her life on her own terms.
A thirty year old man with a teenager has a long term agenda. It is a sinister life-changing horror story for her.