I've found this also- that sometimes talking to others about problems makes matters worse. That you sometimes do get a lecture or utterly ridiculous platitudes. Or, it turns into a contest on how they had or have it worse. The worst thing of all is- I've sometimes found myself doing the same thing to them.
I think in part, people tend to copy the style in which others talked to them about their problems- even when they hated it!
I think the other thing though is that- when we let someone know we are unhappy or, have a specific problem- they may well try to figure out how to solve it. If they can't find an answer, I think this leads to guilt sometimes (in the case of parents- they brought us into this mess at the end of the day,) which then turns to frustration back towards us maybe. Ultimately- why are you making me feel guilty? So, they'll come out with stuff like: 'Everyone has to deal with this sort of thing in life. Everyone struggles. I had it worse than you. What makes you so different/ special?' etc. That's my take on it anyway.
One thing I've found that has helped now and again is to make it clear at the start: I'm not looking for them to provide solutions. Even that I know what the solution is. I'm going to have to deal with it. But- for the time being, it just helps to complain about it to someone! That venting it out helps. I found that helped now and again. To basically say- you can help me simply by listening. Or- possibly further than that- that being criticised further actually makes things worse. You just need someone to listen and react calmly.
Weirdly- people I've found have responded more positively/ helpfully if I've been more positive- well, not positive exactly- but that I seemed like I had a better grasp of what was going on and what I needed to solve it. In my experience, I think that was the crux of it. Basically- I have these problem(s). I'm going to do my best to get over them. To do that- I need you to support me by listening and not getting frustrated/ angry with me.
As for friends though, sadly I think it's kind of rare to find people who will be available to vent to constantly, unless they also feel they can vent back or, they are extremely altruistic or get fulfilment from helping others.
Sometimes I wonder what type of person you have to be to be able to do this. I'd say I was reasonably empathetic. I had a friend who used to vent frequently and voraciously. To be fair, I used to do so back also. Still, it got to the point I found that all I was getting back were increasingly ridiculous platitudes for my problems. I don't think they would have responded well to responses like that. So, I tried to reduce my venting to them but, theirs continued for quite a while. And honestly, it really used to get to me. I'd spend a few hours following a text feeling bad for them. And, it kind of got to a point where I felt like I couldn't cope with their problems on top of my own. I didn't say anything though. That felt heartless and eventually, maybe because I wasn't venting so much, they didn't so much either.
That's the thing though- surely we want people who are empathetic to listen to us but, can empathetic people cope with it ultimately? That's not to try to make you feel bad or a burden. It's just something I wonder to myself sometimes.
I'm sorry you don't feel supported though. As others have said, I think this place is wonderful to give some sense of someone out there listening and sympathising. I hope it can help you in some way.
