This boy i liked now has a girlfriend...?

Don't ignore him. If he knew that you liked him, ignoring him would be showing a sign of weakness. My advice to you would have to be MOVE ON. If he's aware that you like him, your moving on would make him admire you. If he doesn't know, ignoring him wouldn't really change anything. You mentioned this is your 3rd time being "rejected"? Don't let this get you down too much. There are PLENTY of guys out there who'll like you for who you are and this guys relationship might not even last long, who knows?