Can I skip my roommate's birthday party because she's been pissing me off lately?
How is she pissing you off that you want to skip your roommates birthday party?
She's too shy to talk with boys and she cries all the time
If she is pissing you off then you should talk to her about it. She obviously cares about you enough to invite you to the party so you should try to support her and makes her emotionally stronger. Otherwise, you will gain nothing but negativity if you stay pissed off forever.
So you don't think I should skip the party?
No, I don't think you should skip the party. I think you should talk to her about what's bothering you, though, because that's the best way to get things to change.