The people telling you that you are better off single might sound patronising to you but they're also telling you to be careful for what you wish for.
I wouldn't wish for an unhappy relationship though and I wouldn't stay in one... I've previously left abusive relationships. My parent's marriage was unhappy and my mother felt "stuck" as you described. Using this as a basis, I sorted my life out as an adult so I would have my own money and own career and be able to leave if I had to.
I know alot of people in happy long term relationships. More than those in unhappy relationships. My friends who have had unhappy or abusive relationships all got out and funnily enough, every single one of them are now in happy relationships or happy second marriages.
Funnily enough, very few people (usually much older women who had Shotgun type marriages) tell me I'm better off single. It's mainly mumsnetters.
Look I do get it. Take one person I knew from school. Very happily married, she has a good but stressful job (primary teacher), her husband has an excellent corporate career, lovely detached home, fancy cars, 5 star holidays etc etc. And, alongside working full time, she does most of the childcare for their just turned 4 year old and 1 year old twins, one of whom is disabled. She is obviously very stressed and has little time for herself or her interests that she had as a single person. She would love to swap lives with me, she says often.
But would she really? If she knew the gut wrenching pain of knowing time is running out and you might end up childless? When she had to come home to an empty house and an empty bed night after night, year after year? When she has to go on holiday alone or with strangers on singles holidays? When she is solely responsible for all of the finances and becomes long term sick or loses her job? When you are sick for a while and there isn't even anyone to check you are still alive? All that time for hobbies and interests is great until you realise how empty it all feels after a while.
And her problems will ease in time, this is the most difficult phase for her.
It's grass is greener syndrome. Yes, we might both suffer from it a bit. But it is patronising to constantly have the single life held up on a pedestal and to be told repeatedly we should be thankful for a life that feels pretty empty when you have to live it every day with no end in sight.