He'll have left something behind intentionally so he has to contact you to come and get it, it's what they do to intentionally drag out the hurt and pain by them leaving. My ex was abusive for 20 years to me and he decided he wanted to leave after that )probably around the time I had completely stopped giving a shit about him and was staying wrongly for the kids). The first thing I felt when he said he was leaving was relief. Then I had a whole range of emotions: upset, sad, confusion, denial, anger etc. I decided I needed to see a counsellor. She told me it's like the grief of losing someone so you are essentially going through the grief cycle. you will experience this is in your own time, in your own way and in your own pattern. There is no right way or wrong way to go through it, it's individual to you but you will go through each stage.
I think as it's early days you will still have that bond with him and feel quite crap (sorry but I'm being honest), will try to accommodate him, may even want to stay friends so that he is still in your life etc etc. After my counselling I learned that a lot of the messages he was sending me were just to keep me hooked. I started grey rocking him about 6 months after he left, I only whatsapp and I only talk about bills and the kids. Even up until February this year he was trying to hoover (don't think it worked out with the OW he left me for but did't surface til 5 months after he left).
For example, I have 3 dogs. They have always been "my fucking dogs" according to hijm. I do everything for them; he probably walked them about 10 times the whole time we were together. He hasn't bothered his arse to ask about them since he left July 2017 - Feb this year he messages asking if I would meet him with the dogs so he can walk them because he misses them. It's shit like this that stokes my fire and I grey rock his BS like this all the time.
I would suggest if you can get yourself some counselling, even if it is just to go through your thoughts, ideas and feelings out loud with someone, you will feel better for it day by day. Grey rock sounds like an alien concept now but believe me in a year's time it will be your best friend and you will use it a heck of a lot!
I'm wondering whether I will get some BS message tomorrow as it would have been our 19th wedding anniversary 