I'm really hoping to gain some insight and advice as to how to go about doing this. I know it's a pretty small problem compared to others on this board, but it's causing me so much anxiety at the moment.
I started dating a friend before lockdown, but with the Corona virus striking, it was put on hold during lockdown, so I decided to hold off telling the children. Now the new rules about single people have come about, and our relationship can go back to normal, I feel like I need to tell the children, but I'm really struggling with when to do it for the best.
One is 17, and it is her 18th birthday in 4 weeks time.
Me and their father split up 18 months ago, and they had an awful time accepting his new girlfriend last year. He told a lot of lies about his new relationship, and hid a lot from them. As a result, my daughter still refuses to meet his new girlfriend, and she was upset for months afterwards.
My son (13) still does not trust his dad after how dishonest he behaved.
I know I need to tell them, but do I tell them now, which is what I want to do, so that they don't feel like I am keeping things from them? I'm very worried that if I tell them now, then if my daughter reacts badly, it will ruin her 18th birthday in 4 weeks time, which I would never forgive myself for....you're only 18 once! Or do I hold off till after her 18th, but then I feel like I am lying to them for the next month 
It's frustrating as I don't believe children need to know the ins and outs of their parents dating lives, but after how my ex behaved, they were left very nervous about their parents dating again.
I know it's a really trivial problem compared to others, but I'm lying awake the last few nights, really overthinking what to do for the best.
Thank you to anyone that has read this!