Me [19 M] Friend [23 M] Keeps mocking me

Be sure to explain in detail with line breaks. I became friends with the group of 3 people. I enjoyed their friendship and I laughed a lot with them. But I had a problem with one of them and since then he tries to make fun of me in anything (I'm easily irritated type of person). When I talk with girls and sometimes with other people, He joins and start making jokes about me. Especially an expression that I do he keep doing it to irritate me. Now I'm avoiding going out with the group and they started thinking that I don't like them. And they started acting the same. I tried ignoring this guy but he keeps doing it and even that no one laughs (except when I'm With a group of people). I Get overstressed about things and I keep thinking about this and its ruining my mood asap. Any solutions ? Thanks!

tl;dr: He keep trying to make fun of me infront of people and I don't know how to deal with it ?