How does a sensitive/shy guy get the confidence to ask a girl out after being rejected in the past?

Anonymous
So I have a friend and he asked a girl out for the first time when he was 15. She said yes but didn't really mean it because she didn't want to awkwardly have to reject him to his face. It took him a couple weeks of sending her messages trying to set up the date before he understood she meant no because she simply just ignored all his texts. He was young and inexperienced so I don't fault him for not getting it right away. He felt very humiliated once he put 2 and 2 together. Now it's been like 6-7 year and he's 22 and he has never asked a woman out since then. It's a shame because he's very sweet and kind and doesn't hold bitterness or resentment to women for his rejection but he just can't bring himself to step outside of his comfort zone again after he got burned hard the last time he did. He doesn't have an issue talking to me or other girls he isn't romantically interested in but when it comes to a girl he likes he does absolutely nothing in terms of flirting or acting any different from her as he would with us. How does a guy go about getting confidence to approach a woman again romantically?

I want to help him out because honestly it's just kind of sad at this point. I think he's just foolishly holding out for a woman to ask him out and I'm afraid he'll become one of those bitter middle aged dudes alone one day because I imagine a person can only live so long without affection before they snap.
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Bumping the question.
How does a sensitive/shy guy get the confidence to ask a girl out after being rejected in the past?
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