
Yes, he does end up being a green flag. What's important to note that in the universe of the story, dominant alphas need to sleep with people to avoid going insane. Chase is on experimental drugs, and in this point of the story, has only slept with someone once, which was during incident where he slept with Josh.
Now talking about how they fall in love, they basically see each other a lot and Josh basically gives him a handjob when an omega tries to entice Chase by releasing pheromones, and Josh protects Chase by fighting off coyotes after which there is a lot of sexual tension and they do a bunch of stuff and get freaky (they don't go all the way), and Chase tells Josh that he'll sleep with him if he kills someone for him, but then Josh comes to see Chase at some private beach where Chase comes out of the water naked, and they fugg and slowly, the tension increases and they see each other more often. When it is the most evident that Chase has fallen in love with Josh, is when Chase hears Josh talking about Pete and 'Pete's mum' to someone else and realises that Josh has a c-section scar, and then cries and begs Josh to choose him, and tells him that he loves him and stuff.

if u're curious this is the part in the novel when chase cried and beg to choose him https://blsnacks.wordpress.com/2021/08/12/kiss-me-if-you-can-volume-3-chapter-14/
i’m so confused what’s happening can anyone who read the novel spoil me on how they fall inlove and if ml is a green flag