I'll admit I was kinda going through some shit when I wrote my initial comment. So I will clarify by saying that nostalgia is real, and can absolutely be a good thing (in fact it is psychologically necessary) but it can also sometimes lead to an unhealthy romanticization of the past. I do think that Chase and Leo could still have a future together, but it would take a great deal of work on both their parts, especially after the events of Leo's arc. I believe that the healthiest option is for them to admit that though they still love each other a relationship is simply not in the cards.
I won't say it's impossible. The romantic in me still believes in the power of what they had but I think that the ultimate moral of this story is "you gotta know when to fold 'em". That as painful as it might be, sometimes (not all the time, but sometimes) the best thing you can do is let go, move on, and try something new.
I was talking to a friend about Echo and I summarised the relationship like this: "Contrary to popular belief, love is not all you need. You also need trust and communication. Leo is bad at trust, and Chase is bad at communication." And therein I think we can identify a formula for fixing their relationship. And if you want to follow that line of thought then go ahead. I'd like to believe that there is hope, I'd like to believe that love can withstand anything. But ultimately we all take away what we need from a work of fiction, and at the time I personally really needed a story about letting go of the past.
I hope you are well, and I hope I didn't cause too much of a stir with my first comment, I was in a fairly emotionally charged state at the time of writing.