"Since" is used to talk about something that has happened after a certain time in the past.

You use "since" with "have":

I've loved him since I was 10 years old.

Haven't you eaten anything since lunch?

You don't use "since" with simple past tense verbs. Remember this! For example, "I loved him since I was 10" isn't correct.

If you were just talking about a point in the past, you can say "since then":

I moved out of my parents' place in 2003, and since then I've lived in 6 different apartments.