How the hell people make friends????

My friend count is really low. If I take away family and boyfriend, the number is 0. ZERO. So yeah, that leaves me with mom, sister and boyfriend on my circle of friends.

I have college and work colleagues, but nothing more than that.

Anyhow, my question is: how the fuck are people supposed to make friends????
For instance, I'm shy and a introvert, so I get intimidated when I want to join a conversation about a topic of my interest. And also I feel like if I join, I might be interrupting or invading an existing group of friends.

I recently realized that I need to make friends urgently. Occasionally I feel alone, but the future might be even scarier if I stay like this. What will happen if my bf and I break up? What will be like when I move out of my mom's house?