"Conflict" has a specific meaning in literature. Your main source of conflict is the relationship, but conflict means what is keeping the character from what they want.

Your summation of the story seems to be more events that happen then a plot. This is what having an antagonistic force does; it unites the events that happen and make them work in the whole picture.

The problem lies in the fact that conflict isn't the sort of thing that you can shoe-horn in. The past and how the characters handled the conflict will colour their POV each time an event occurs. So going back and adding in specific scenes of conflict will still mean that when there is no rewritten prose, you'll have characters who don't react to what has happened.

In order to make major changes, like adding conflict or tension or changing the character's motivation -- even if the plot itself doesn't change a bit -- means that the microtension from within the prose won't fit. You're looking at a major rewrite. Don't even open the document. Rewrite it from what you remember and I'll promise you it will be a hundred times better than if you use spit and elbow grease trying to save the prose.

But don't rewrite it yet. Write something completely different. Give yourself the mental space to clear out what you think you did with the story. Don't even write the sequel. When you go back, it should be with a completely fresh set of eyes.

The hardest thing to learn in writing when you're just starting out is that your finished draft, the one that took months or years to do is just your best guess and what has happened. Since you haven't gotten to the end yet, you don't know which scenes are important, which scenes need to get cut, and which scenes are missing, under-developed, or bloated.

Some writers go a decade not figuring this out. Some writers never figure it out. Before everyone had PCs (which was only 20-30 years ago) when you go to the rewrite phase, you rewrote it. Your prose gets tightened up, you know your characters and your story far better than you did when you sit down, and your finished product is what you meant to say, not what you actually did.

And unpublished writers still think all of that is a waste of time. Getting a perfect first draft that deals with all the dozen aspects of story right the first time is like winning a grand-champion poker playing tournament the first time you play. You can keep hoping for that to happen, or you can buckle down and get started on that potential future now.