Alexander Buchanan attacked the trio who were unaware of how each other suffered.
It was only in 2017 that the victims bravely went to police to report the 62-year-old.
A judge heard how one feels “a weight has been lifted” after Buchanan was held.
Buchanan – also known as Sandy – faces a lengthy jail-term after he pled guilty today to sexually assaulting the three boys.
He was remanded in custody as sentencing was adjourned until next month.
The crimes occurred between 1970 and 1977 at a house in Falkirk.
The High Court in Glasgow heard all three victims were attacked in a similar way by Buchanan.
One told a relative years later what had happened.
This victim later said: “I have held it in for all these years. It feels like a huge weight off my shoulders.”
Another recalled feeling “frightened and ashamed” at the time.
The court heard he later stated: “I have a good life, but I have times when I am moody.
“It is something that is always there. It sometimes gets in your head and I just want to scream.”
Buchanan, also of Falkirk, was arrested and initially “denied any wrongdoing”.
But, he went on to confess abusing the boys – claiming he was now “sorry”.
Buchanan’s lawyer today asked for Buchanan to remain on bail.
However, Lord Burns remanded him adding he had “pled guilty to serious offences”.
A woman with Buchanan left the courtroom in tears as he was led handcuffed to the cells.