The usual way 1 on 1 hacks like this occured is simple password guessing your exkniw a lot if iersibal info, ebaikaddresses, Twitter and Instagram handles and dob. He very probably fucked through a few common things he knows about you to second guess your password
Invent a string password for yourself, the are plenty of mnemonic techniques to help you plus simple cypher substitution and special chars
For example take a phrase like,
My eX Boyfriend Is A Creep And A Total Gimp, Plus He Is Useless In The Sack
that becomes
MXBIACAATG,PHIUITS
then do l33t vowel cypher substitution
a=4
e=3
I=1
o=0
u=4
it then becomes
MXB14C44TG,PH141TS
swap the comma for a hyphen
MXB14C44TG-PH141TS
then drop to lowercase
mxb14c44tg-ph141ts
some password require an uppercase either the first it last letter. it satisfies both Apple, Microsoft and Google for strong passwords, plus it's easy to type in on an iPhone or Android phone.
every time you need to enter or create a password say to yourself.
My eX Boyfriend Is A Creep And A Total Gimp, Plus He Is Useless In The Sack
consider changing it every few months.
finally enter your email into
haveibeenpwned.com
you'll see all the sites that have been hacked and where your password has been stolen
As a suggestion go around those sites either delete yourself or change the password.
I know the password stuff looks painful, but after doing it for a while it becomes second nature.
Protect yourself online