In your opinion what causes christians to believe in Jesus

[Sheldon]

The difference is that girlfriends are real things. To put them on a par with a non-existent thing is just silly. It’s like saying someone has a ‘relationship’ with the Invisible Pink Unicorn.

A pink unicorn is different in that it is rather impersonal, it doesn't quite have the social relational aspect. 

In the same way the deities people have imagined are to me. I have a relationship with people, not necessarily with what they imagine to be real.

With religion, I think the effect is so strong it even spills over from the pulpit to the pews. I think people are also more or less likely to believe based on their interaction and relationship with other followers. A person treated badly by christians is more likely to not believe God exists, and a person treated well is more likely to believe he does.

Ah another claim, ah no pretence of any objective evidence to support it, I am going to go ahead and apply Hitchens's razor here, slash...and disbelieve this entirely unevidenced claim. 

NB What you have described is a relationship with theists, not with their imaginary deity. If I was beaten up by a load of Star Wars geeks for dissing the franchise, it would not register as a reason to disbelieve any claim that Jedi are real, I already have sufficient reason for that, as I do with deities. Now I can't claim to know what others think, unless they tell me, as you keep doing unabashed and without a hint of irony, but I am an atheist, I no more have a relationship with deities than I do with a flat earth, and for the same reason. Though I occasionally have to listen to people pretend they exist.