Getting a diagnosis as an adult can be hugely beneficial. I was 21 when I was first diagnosed with dyspraxia, I'd left Uni so wasn't getting support for that. I'd masked my problems so well. Teachers had noticed some of the individual problems and helped me to cope, e.g. organising myself etc. I'm very organised now as I've adapted. They were always a bit puzzled as to why I always got a grade lower than expected, I was seen as bright but 'lazy' which teachers frequently called me. Now I know I'm NOT lazy, I know why I struggle with so many things, but also why I excel in other things.
It's helped my relationship, DP knows I'm not lazy, he knows I genuinely forget things and now he knows to believe me when I say something wrong (I have strong ASD overlap) and am genuinely bewildered that I've annoyed him/been offensive. It's helped with parents and friends too - they know I'm not being 'difficult' or 'quirky'. I was often seen as being weird for the sake of being weird, we now know it's not true. Plus I can 'see' SN now more and more in others, one of DP's mates has some odd behaviours and like me takes language very literally, for both of us 'did you sleep with them?' means - 'did you sleep in the same bed?' not 'did you have sex?' - DP said it's improved his friendship as he can see now that his friend may well be on the Spectrum too and he accepts his eccentricities better.
It's enabled me to receive extra help searching for work via Remploy and having the official diagnosis means I can explain any difficulties to employers and ask for reasonable adjustments such as written instructions, being allowed to make to do lists etc. I persuaded my GP to send me to be assessed because I was struggling to get a graduate job - I just couldn't pass the maths tests and was being screened out at the 2nd stage with every job. Having a diagnosis meant I was able to request extra time etc for the tests.
But most of all I am finally at peace with who I am, I spent years knowing that something was wrong. I've found old diary entries from my childhood where I've said I was sure I had an undiagnosed medical condition, I just didn't know what. Now I know that I'm not lazy, or stupid, or hopeless - I know now that I'm bad at PE not through lack of effort but due to poor co-ordination, I know why my maths is so abysmal and I know now not to care so much about what people think - I can look back on grades I used to be ashamed of and know how well I did to get them and to get my degree despite having an undiagnosed learning difficulty. I've stopped comparing myself to my NT peers with much better grades and skills as the comparison is invalid - they simply were not blessed with my brain 