What exactly was it that attracted Ron Weasley to the young lady most people wanted Harry Potter to end up with, Hermione Granger?
It was a couple of contradicting points; he was probably always concerned he might look a fool in front of other young women.
The contradiction is that once he met a girl who thought the world of him in Lavender Brown, he then couldn’t handle the pressure of being Mr. Perfect.
“Fanged Frisbees are banned…” she (Hermione) told… …The scowling boy… …Ron waited for him to vanish, then tugged the Frisbee from Hermione’s grip. “Excellent, I’ve always wanted one of these.” Hermione’s remonstration was drowned by a loud giggle; Lavender Brown… …found Ron’s remark highly amusing. She continued to laugh as she passed them, glancing back at Ron over her shoulder. Ron looked rather pleased with himself. Harry Potter and the Half-Blood Prince – J.K. Rowling
Ron always suffered from an inferiority complex; he could never meet the expectations set by five brothers and he lost the baby of the family position to Ginny Weasley.
That left him with self-doubts the led to underachievement.
Ron’s position as the right-hand man to Harry Potter went a long way to boosting his image and his confidence around other young men his age, but as far as the romance department went, that was another story.
When Ron began his fling with Lavender, it was outside his comfort zone; he had never been in a place where he was in complete and total control of a relationship.
And Ron didn’t like being the sole captain of that ship.
Hermione accepted Ron’s unwillingness to dominate a relationship and we all know Hermione preferred to be in charge anyway.
She was safe; she knew his flaws and he knew hers; between them, it was a safe union, one that kept them both in a comfortable relationship, if not really an exciting one.