@Vodkaany1 has stated that they have experienced alcoholism within their own family. A lot of people who haven't seen alcoholism or other addictions up close don't realise how devastating this can be. The UK minimises heavy drinking as normal culture, and this can be hellish for anyone trying to protect a loved one with a genuine drinking problem.
I don't think the OP is coming at this from a place of judgement, more a lack of knowledge about the issues facing homelessness, and a lot of personal lived experience of feeling helpless whilst a loved one drinks themselves to death, whilst those around minimise the problem.
The OP tried to help, it didn't go they way they expected. They've tried to help people dear to them before and it hasn't gone the way they hoped either. You can understand questioning the interaction, and wondering what they could have/should have done differently to get a better outcome.
As a lone person (I haven't assumed the OP is female, but the odds on this site are the OP is a woman), the request to take cash out would have immediately made them feel vulnerable, and that would have informed the rest of their interactions. When you don't feel safe yourself, you act on adrenaline and you're not entirely sure if you made the most logical decisions, because you weren't your usual self at the time; you were yourself on high alert.
The OP had the kindness to actually stop. A lot of people don't.
People are allowed to put boundaries around their kindness. In fact, I'd encourage it. If you have to do everything or nothing, most people will opt for nothing. When people are allowed to determine the level of support they give to strangers, they're more likely to do so, and the world is a less shitty place.
You might not be able to afford to or want to give £100k to Crisis. You might have the resources to stick 50p in a charity tin. Just because you can't do the big gesture doesn't mean you should skip the smaller gesture for not being as good. You do what you can, and what feels right to you. When you're kind within your own boundaries, you don't feel taken advantage of, and you are able to later repeat that kindness, because it feels safe.
Small, kind gestures all add up. Don't ignore their cumulative effect.
And I don't think it's kind to judge the OP, who tried their best. I hope they'll take on board my previous comments on Street Link, and learn from this encounter. Not because I think they're an awful person, but because I think the way they helped didn't make them feel safe, and when you're being kind, you deserve to feel safe. That's not something you should have to give up when helping.