I have only ever had relief at leaving a relationship as I've been seriously unlucky with men, but my partner has had his life turned upside down by the person he thought was "the one".
They were together for almost a decade, were engaged, had a 1yo son and a house, good incomes, 2 cars, regular holidays, he was working towards a really good job by doing half work, half uni (back in the day where that was much more common) .. and then suddenly, she told him she was leaving, to go with someone else who she had been seeing.
Him and their 1yo son were left. She was the love of his life, everything seemed perfect. He was left to care for the child alone, so had to leave his uni course, so was stuck in the job he'd had with no more chance of promotion - so you're looking at full time, distance travelling, for £1,200 a month, when it would have more than double that after training - if not more!
He plunged into a deep depression, and his relationship with his son suffered, he couldn't trust women, he wasn't taking care of himself or his house, he stopped seeing his friends.
Now, 15 years later, he still has problems. The main one was how much it set his career back, as he was looking after a small child on his own - so he never got the chance to go back to uni, and by the time he could, the courses were completely different, so he couldn't earn and train at the same time.
He also really struggles in relationships. He keeps a huge part of himself held back, and won't give women his full emotions in case he gives it everything he has again, and she leaves him.
This resulted in him "settling" for a woman for 8 years who he didn't really love, and was more of a mother to him if anything. It seemed to suit her too, but eventually he'd had enough and split with her - which was even worse for his son, as he'd seen this lady as a mum more than his actual mum. So that caused a load of upset.
Then when he got with me, a year after being single, he was so, so cautious (as was I after my previous - so in many ways it looked like we were doomed from the start!) and he warned me that he really struggles with affection, he only told his ex he loved her twice in 8 years (while pissed - because he actually didn't), and he didn't know if he could let himself fall for me.
It has been a long road for us, BUT, he will now tell me he loves me sometimes. It's easier for him over text, but he does say it to me when we're cuddled up in bed too, which is always a really nice surprise. He does still struggle with affection, and sometimes he even seems to tense up if I want to cuddle while watching a film or anything, but every month that passes I feel him relaxing more, and things getting easier.
We've been together for almost 2 and a half years now, and live together. He has a long way to go, but I see a huge difference in him now since we met, so I hope that finally we can build the life together that we both deserve after going out with the people we've been unlucky enough to meet before!