Hello Mooky,
I'm sorry you're feeling this way but I can assure you that you're not alone - it's a very natural reaction to the transition from being with your baby 24/7 to spending regular time apart.
I'm a LP and I went back to work full time when DS was 8 months (now 19 months). This was very hard for me but DS has only thrived over the last year.
DS spends his week days between nursery and ex-MILs and I think that the varity does him good. He is very outgoing, loving and sociable and has some fantastic little friends at nursery.
While I have all the respect in the world for SAHMs, I knew that it wasn't for me. Whilst on mat leave, I did my best to ensure that DS had the most varied, fun filled, educational days possible but there was a limit to what I could do. Now that he is at nursey, he has access to such a wide range of people and resources which I think benefits him so much, as will your DD's time with her CM.
I of course miss DS terribly when I'm at work and IME that doesn't go away (I wouldn't want it to). Throwing myself into my work and enjoying it during the day is what gets me through. Plus when I collect DS in the evenings, the huge smile on his face, kisses, cuddles, artwork, baked goods and endless other presents make it all seem worth it.
My advice goes without saying - treasure every moment. My mornings / evenings / weekends / days off with DS are so special and if anything I probably appreciate these times more now than I did when I was on maternity leave.
I know our situations are different and that you are going back PT. I know if it still a terrible feeling though when you drop her off for the first time.You've mentioned that you are happy with your choice of CM which is so important. Just try to take one day at a time - enjoy being back with your work mates, have a fun morning catching up on the gossip. Call the CM to put your mind at rest if needed. Think about all the things that you and your DD will GAIN from the new arrnagement and finally give her the biggest kisses and cuddles when you collect her.
Best of luck on Monday. 