Oh Connie, you've described me perfectly! (Congrats on the birth of your DS2 btw.)

There are days where I've had to spend a lot of time with DS and DD just says "Mummy, I miss you." It kills me. Nights aren't usually too bad, Daddy always does it. But last Wednesday he got called in to work and I did the bedtime thing, brushed her teeth while feeding DS and then juggled him and books until I couldn't anymore and just sang to her. She was ok, but I felt bad I couldn't lie down and snuggle her like I normally would. Then tonight she wouldn't sleep for DH, after half an hour she was calling for me. I went in, again feeding DS. It took an hour. It's not what she wants so I feel bad

There have definitely been tears (mostly mine), but it's a matter of balancing - you can't be there every second for DS1, or for DS2. You just need to work out if you can do both at that time, and if not, who needs you most.

Big hugs, it will get better