Shino never had a girlfriend.
He once had a crush on a girl in ninja school. He bought her a flower and decorated it with pretty things. When he gave it to her, she ran away and screamed. He looked at his desolate flower which was coated with pretty little bugs and wondered what was wrong.
Another time, a girl tried to kiss him as a dare, but then she started crying when she bugs crawling out of his mouth. Shino still wondered what was wrong.
Girls must not like him, he thought. So, he never liked another girl again.