First of all, you can "accept the responsibility" without having to stay as a couple. That is not being selfish.
Now, I don't know if having the person who created a life-changing problem solve can be something to be happy about. I think it's something to be expected. What she did was beyond bad. It was really twisted. But let's move on to the uke. You said "not be selfish just because he loves the seme" but it's kinda his whole character in the manga. He's willing to disregard the seme's feelings and cruelly stay by his side, date a girl to keep a facade up (albeit the girl in this case is somewhat to blame, since she knew her position). The uke is nothing but selfish the entire manga.
Well you're right. Its just I'm thinking that atleast he is not selfish enough (but he really is selfish) that if ever they really have a child he'll live the kid and not atleast let the kid have a family with a father in it. Btw thanks tho kinda changed my view to the uke
I know what Mako did was wrong but I'm atleast happy that she confessed that she's lying. Maybe its nice that she lied about the pregnancy since it kinda made some impact on how the uke and seme will accept stuffs between them. And I'm also a bit happy that even though the uke really loves the seme after knowing Mako is pregnant he is atleast is willing to accept the responsibility and not be selfish just because he loves the seme