I found out yesterday that Ale and I are hanging out on Saturday for longer than I thought

It was like:

Me: *buying chocolate bars from him*
Me: *hands him the money*
Me: So quick question.
Ale: Yeah?
Me: That party on Saturday. Who's that for?
Ale: Me. Since my birthday always falls on a school day, we rarely do anything for it, so this year, we're going to have a little late birthday party since everyone's gonna be here.
Me: Oh okay.
Me: W-would it b-be okay if I stayed a little l-longer on Saturday for y-your birthday? **
Ale: Oh yes! You were anyways!
Me: I-I was?
Ale: Yes!
Me: Thank you!
Ale: What kind of boyfriend invites his girlfriend to his house, then kicks her out when the party starts?! Y' might as well just write "Dickbag" across my forehead in permanent marker if that was the case!
Me: Well I thought that your party was a "Family only" type of party.
Ale: If it was, I woulda just bagged the fuck out of my parents to let you come. If Car was family when she dated Noa and Lha was family when she dated Jak, then you're family cuz you're dating me. So if it was a "family only" party, you'd be invited because you're family.
Me: *mentally* dON'T YOU FUCKING CRY, YOU WEE LITTLE BITCH-
Me: Awww!!

** My Mom was pissed that he was having a party and didn't invite me (as far as we knew), and I told her "Look, if he doesn't invite me, that's fine. I mean, my birthday party is gonna be at my grandparents house on my actual birthday, and he can't come. So it all works out." So she made me ask if I could see what the deal was with the party, and ask if I could stay for the party.

Here's the deal: I HATE inviting myself  or asking if I can come to things!! It feels rude to me, and I feel like I'm imposing on something if I do ask, and I feel bad if they weren't planning on inviting me and then I ask if I could come then they have to say "No". I feel better if it's "Invite only". Then there's some times when my friends will go somewhere (like to the pool or in the elevator after choir) and I'll stand there and ask "Can I come?" And they go "Yeah!" In like a "Duh! Yes! Where else would you go?" tone and I sit there like "I just didn't wanna impose..."