Tell them the truth is always better. I have lied to my wife of 27 years and know I am all alone.
Yes you’re right. Ultimately you made an error of judgement, it’s only human. Whatever lie or lies you’re referring to, even if it’s 27 years late, it might be good to tell her the truth now, assuming you haven’t already done that. I know that if I was in a relationship with a partner who had been lying to me, I would want the truth even if it hurt terribly, and I’d want it as soon as possible, EVEN after such a long time - because at least that would give me the opportunity to feel aggrieved, to try to process the harm that had been done to me, etc. It may well be brutal, she may hate you, she may feel cheated, she could die of a heart attack from the grief, but I still think ultimately the right thing to do would be to tell her as soon as possible. You can’t change the past, you can’t change the fact that you lied for 27 years, but you CAN change what you do in future - and that wouldn’t entirely erase what you’ve done, but it would put you one step towards healing and moving on. Congrats if you’ve already told her, if you haven’t told her, I hope you’ll think about doing so.
Nobody is ever truly alone. Every step you make towards honestly engaging with people is a step towards intimacy and love. As emphatic as I am about HER needs, I’ll also say that whatever you did, I believe one day can be healed and forgiven, so don’t hate yourself and don’t feel cut off from humanity. There are people who’d murdered others, people who’ve lied to millions of people. All of us if placed in another persons circumstances would have made the same decisions. We all experience trouble in love, who can really claim to be truly innocent? By most ‘common’ standards 27 years of lies is significant, but most people are petty common liars or hypocrites in other ways. You could almost say that we’re liars by nature, but it’s a good thing to overcome this nature when we can. Don’t stress.
Best of luck either way. Best wishes to you, lots of love.