I have a love-hate relationship with Echo.
You're correct, there's no good ending where you end up with Leo. But that didn't bother me, especially after playing Route 65. I highly recommend replaying Leo's route (totally worth it to skip all the dialogue until the final choice of leaving Leo or staying with him) and choose to end the relationship. My soul was uplifted with that ending. Probably Chase's too, but you should make up your own mind.
On Flynn's route in Echo is that he says to Chase something about how Leo took advantage of him because he was so young when they started dating. That'sexactly what Leo did in Route 65. Here's this 15 year old kid who's just coming to terms with his sexuality and in swoops this manipulative, explosive (anger) college boy who controls every part of Chase's life. I didn't find Route 65 romantic at all, honestly... I've been in relationships with people like Leo. They're emotionally abusive. They alienate you from everyone you care about and force you to only be with them 24/7. They get jealous at the smallest things and will beat anyone they see as a threat. Leo doesn't love Chase. He sees him as a possession. He's like a trophy. He won't even let Chase leave when that's the only way for him to be happy in the long run, even if Leo was suggested to go with him.
I mean, Chase says they'll work it out, but Leo grabs him from the train and when Chase's feet get cut off he doesn't even get him medical treatment, he just holds the otter until he dies. I bet Leo turns into Norman Bates (Psycho the movie; Bates Motel the series) and keeps Chase's dead body around pretending he's still alive.
I imagine Adastra is going to be a romantic story. There's nothing dark about it.
It does sound like they may do a prequel, but I'm not sure. This is based on Adastra being mentioned in Flynn's route in Echo.
I just started Repeat. It's really interesting. It has dark elements, but it's not at Echo level darkness. I finished what's available of one route, 2-3 more to go. New updates should come this month.
Project Aego seems to have been abandoned. No updates in 2 years. It's sad because it had great potential.