I know it's hard...believe me...but it's the latter...I know it blows to pretend to be cheery but it will help your mood in the long run...pretending to be happy is far more likely to contribute to you actually being happy than showing the world how you feel and dealing with the repercussions of that.

Trust me on this, I'm on year 43 of this shit and it took a lot of lost friendships before I finally clued in that people are mostly interested in their own problems and are hanging with their friends because it's meant to be fun. When I was a dark cloud, I'd stop getting invites then feel worse about myself and that would start a spiral.

Pretending is exhausting so maybe go out less. Or say you can stay for X hours (whatever you can handle). Way better to pretend to be happy for two hours than show them you are sad for four.