A long time ago, I tried giving similar advice to someone on reddit I saw had a similar vibe I felt I probably had some version of back in my 17 - 22 age range period. I think telling someone who feels hopeless about their own chances in relationship success stories where you personally can relate are the best way to pull someone out of an otherwise toxic spiral they often get stuck in.

Not the typical "be yourself" parental type advice, but like "I also felt" and "well until I" type of personal experience perspective. Use your own genuine growth and self-reflection as a cornerstone of how you talk to them. If you want to help, you need to talk to them in a way that makes them feel like they're not the only person in the world who is experiencing or who has experienced the sort of despair they have.

And - as someone else pointed out - it isn't your responsibility. And ultimately, the person has to themselves want things to be better. If they've decided it's hopeless, there's nothing anyone but themselves will be able to do... but it is noble to try.

At one point in my life, I had decided I would stop feeling hopeless after being rejected by those who I had fallen for, and instead work on myself. As a result, I ended up getting into really great shape, going on dates, and meeting lots of really wonderful people and growing as a person - ultimately finding someone who I eventually married and had a family with. I realized far after the fact that I must have been someone miserable to be around in at least some way - due to the way I was raised (also religious Southern sheltered family), and the poor socialization skills I had lacked as a result.