How do i come out to my mom

ok so She knows i'm bi i've dated a boy before but it was right after a breakup with a girl. so she thought maybe i was just confused because i really liked her. Now i'm with a boy who lives in a few states away from me. I visited him once but i told my mom it was for a convention which it technically was since we did go to one. I talk to her alot about him and i just wanna come out and tell her soon so he can come visit my family and I but i keep getting too nervous about starting up the conversation. sorry for rambling