Even if Sera is now in a trio with Ene and Lulu, the two still have their own bubble. I wondered why, I mean, they love Sera enough that if Sera ever needed the same help Rika did they would absolutely help him. If Sera ever needed to be saved from kidnappers they would absolutely bribe, threaten or leave the country to find him the way Lulu did for Ene. Ene and Lulu are ride or die for Sera, too, so why is Sera different.
Sera is different because he wouldn't bend the law or abandon his people for Ene or Lulu. That's always been their difference anyway, I guess being besties wouldn't change that fact. Sure, Ene and Lulu are ride or die for Sera but Sera can't do that for them. This is something Ene and Lulu knew about Sera without him needing to say anything and this is something they never demanded him to change so no hard feelings.
Sera would feel bad about it though. Ene isn't mad, Lulu isn't mad, they weren't disappointed. They never had any expectations from him.
If Sera were a boy who wants to be relied on, if his issue was self esteem or self worth, finding out that his BFFs never trusted him to do anything would have been more devastating but alas! His issue is his very smol social circle.