clingy ex

So I just needed a bit of advice bc I'm in a bit of a muddle so, I've been with my s.o for not too long, but I know he's the one, like we're ready and planning to get married in the future and I just know he's the one, I've jumped many hurdles to finally find him and he see's all the perfection in me including my flaws and I've never felt like this with anyone, so recently I changed my instagram dp to me and my s.o and my ex , who I only found out recently had been spying on me, and once he saw that pic ( my ex and my close friend are friends) he messaged my friend asking who my man is, this didn't get to me bc this whole situation is just plain immature and I've moved on and I'm finally happy, so just a few moments ago I find out that my ex actually took the time to search my followers I don't know how, and ended up finding my s.o, and ended up calling me demanding me to tell him if I'm going out with him and his age since  my s.o is few years older then me and my ex isnt, now I know my ex is jealous that he messaged me friend saying ' I'm still better looking than him' now I'm not one to sink to his level, but I just don't want to be involved with him anymore bc I'm so happy with my s.o I'm just so confused, bc my ex is stalking me and claims he doesn't care yet he's going to certain extents to find out who my s.o is