So you were with guy x, broke up, started speaking to other guys on tinder who you added on snapchat, turns out some of these were x's friends. When they asked you about your previous relationship, you said some not very nice things about x and relationship. You are now back with x, but he won't tell you who the guys are on your snapchat that are his mates.
After that I'm a bit lost to what is going on, sorry. Is it
a) that you deleted snapchat at his request, only to add it again later and then his mates told him?
Or is it
b) that some contacts were accidentally deleted and you re-added them from your phone contacts, and some of the ones you re-added must have been his mates, who then told him?
It sounds from your post more like b) happened, however he then says you're back on snapchat, which is why I wrote part a). Did he think you had deleted snapchat? Did you lie and say you had but you hadn't? If you hadn't, didn't his friends know? Sorry, I'm a bit confused.
TBH either way it doesn't sound great from either of you OP. If you are happy in this relationship, why do you need random guys contacts that you met on tinder? However he also sounds jealous, controlling and insecure to be checking up on you, getting reports on you from friends, potentially getting his friends to add you as well when you broke up to spy on you effectively (that's what it sounds like anyway).
Can't really advise further, hopefully someone else will be along to help.