<human>: So yesterday I was speaking with my father and he told me that he was going to break up with his SO, when? I don't know, he neither. 

She have have been thinking about his 60's for over a year and organizing a  surprise birthday party for months, inviting family, finding a place, etc... (I don't know how much preparation it's done, I haven't participated in the organisation).

I'm the only one who knows he told it to me in confidence, one of my sisters also participated contacting family members to come. so I don't know if I should tell her. Of course won't tell to his SO.

Should I ruin the surprise party and tell him about? should I lets things flow and don't intervene? his birthday is next month. Also I don't know if he would tell me once it's done.

Can you condense the text into a few key points?
<bot>: My father (59) is going to break up with his SO of 3+ years (~60F), she have been organizing a surprise birthday party for his 60's for months. Don't know what to do.