Klaus and Dave need to be reunited in The Umbrella Academy season 3. Klaus Hargreeves met Dave Katz when he accidentally time traveled to 1968, landing right in the middle of the A Shau Valley during the Vietnam War. The Netflix series doesn’t dedicate a lot of screen time to the pair’s budding romance in season 1, but Klaus and Dave do fall in love while Klaus is time displaced. While things don't end well for them, the cliffhanger at the end of season 3 suggests Klaus and Dave could see each other again.
Dave ultimately dies during battle in season 1. Traumatized by the event and unwilling to allow Dave to die unnecessarily once more, Klaus attempts to prevent him from enlisting when he returns to the 1960s in The Umbrella Academy season 2. Klaus is haunted by Dave’s death and it’s something he clearly carries with him throughout season 2. After all, Klaus doesn’t expect to have witnessed his lover die in his arms on the battlefield. He and his siblings have already messed with time before, what’s one more change to the timeline? Seemingly destined to return to the 60s, Klaus works to ensure Dave’s survival.
Knowing that he enlists for the Vietnam War on the same day John F. Kennedy is assassinated, Klaus tracks him down ahead of time, imploring him not to go to war at any cost. Unfortunately, it seems Klaus’ attempts to thwart Dave’s death backfire and he winds up enlisting ahead of when he is actually supposed to. But, all hope isn’t lost. Dave enlisting early and the Hargreeves arriving in the present timeline to discover that their dead brother Ben and father Reginald Hargreeves are suddenly alive means that everyone’s fates could now be different. This includes Dave.
It’s possible that enlisting for the Vietnam War earlier than expected means that Dave somehow survived and went on to live a full life. With an alternate timeline, anything is possible. In that vein, the chances of Klaus running into Dave are higher than they previously were because of the alternate state of events. Of course, if Dave is still alive, it means that he’s five decades older than Klaus remembers him. While The Umbrella Academy season 3 will probably not include some epic romance between them with a potentially huge age difference, being able to see that Dave has lived a full life could be good for Klaus.
Perhaps the former lovers will reunite in the present and Klaus can finally be completely honest with Dave about everything that has transpired. If the Hargreeves will be trying to set things back to the original timeline, then Dave won’t remember any of it afterwards anyway. It’s likely that Dave will remember Klaus and the advice he tried to give him in the 60s. Dave potentially being alive could also genuinely develop his and Klaus’ relationship. The pair got a bit more time together in season 2 than in season 1, but it still didn’t feel like enough. Without the obstacles of enlisting or going to war, Klaus and Dave can sit down, be present, and have a conversation in The Umbrella Academy season 3 — hopefully, one that can offer some kind of closure for Klaus.