It's okay if they're blood related as long as they love each other. It looks like they care for each other a lot. I hope Helios and Anonymous198958 get to experience that kind of love from their fathers one day.
If I remember, I read this a long time ago and it didn't have a full ending yet. I'm really hesitant to try again because if it ends at the same point I know I'm going to be really dissatisfied.
With all the NTR on here I think this is the furthest from betrayal you can get. He's giving his friend a new dad.
And my axe.