How do I cope?

I completely agree with both the posts above mine.

I suggest that the OP, finds a quiet spot and cries her eyes out until she can cry no more and washes all her sadness away, then washes her face, has a nice cup of tea and decides what she wants to do next.

I recommend a good walk looking around and and seeing all the spring flowers that are coming out at the moment, a promise of spring and new life. Treat yourself to a bunch of daffs or favouritw chocolate bar, then, when she gets home she can sit down and plan her own new life.

I’m pleased you answered before me BB. In the absence of any unmentioned health problems, my ‘advice’ to the OP was going to be ‘pull yourself together!’
There’s a life out there to live, you only get one shot at it - go for it and stop living it through your DD and DGD. Surely you didn’t think they’d be there for ever?

Oh dear I’m sorry that you’re so sad, but she’s just ACROSS town many of us on here have our grandkids the other side of the world !!
Please stop thinking it’s the end of your life and start looking how to fill it with other things you re still going to be very very close, so you’re one lucky lady.. nothing could be worse for your daughter and granddaughter than you being so clingy
only you can change it, no one can do it for you and you have to stop putting so much pressure on them
Do you work, have a husband, have friends, hobbies ? If so you heed to have a big push at them if you don’t then you need to find all these other outlets for your life and energy and mental health if you sit moping because they ve moved a few miles away you are going to be NO use to them or yourself

Stop putting this awful pressure on your daughter and grandchild everyone has to be free to go where they want and make their own decisions Sorry if I sound hard but you really need to give your head a wobble.