You don't know what most people do.
It would be nice, but he currently isn't doing this.
You wrote:
"I last saw him on the 23rd in person and he hasn’t replied since then but has been on WhatsApp loads. I’ve sent him Merry Christmas today and had zero reply but he’s been on instagram posting his Christmas and has been on WhatsApp a lot. (I stupidly keep checking if he’s replied and it’s always he was online 20 mins ago for example)"
Constantly monitoring his online presence, and posts is cyber stalking...even though you feel it's not.
Checking once to see if he is still amongst the living was okay. ..because of concern. . In the last two days you admittedly revealed that you know that he has used the app a lot, "loads" has been online a lot, has posted, that you check often and every time you look his active status always states that he was online 20 minutes ago.
That is obsessive behavior and cyberstalking.
A lot of posters have started threads about some men doing these things such as the online stalking, and those men are bashed, insulted, and called creepy..tell some women they need to report this to the law and get orders of protection, etc...
....but when some women do this, a lot of people don't hold her accountable nor in the same regards.. they tell her it's perfectly acceptable..that she's not doing anything wrong..
Well...it's unacceptable for anyone to exhibit this type of behaviors and cyberstalk.
If you don't like what you feel like he's doing..and what's happening..
Disengage, block, and work towards moving on.