He ignores some of my fb messages, answers short but totally different in person, why?

[dogman]

Facebook is basically a public forum. You seem to be so into fb that
you cannot understand someone who cares for you. He expresses
himself on more private venues. As you know he is busy studying.
Apparently when he studies that's where his concentration remains.
Cute or funny messages can be annoying when they interrupt more
significant actions such as studying.

Stick with your love of fb for use with your more casual friends.
YES some people do really think like he does (I'm one of them.)
Are you a woman or a little girl? From your examples you ignore
his feelings on the subject. Remember too that his concentrated
studying enables him to see you on weekends.

Instead of feeling ignored and considering him as rude learn to
understand and appreciate him as he is. You can communicate
with practically any fool on fb.