You have your timelines all screwed up. So far, I've only encountered one path in the present timeline you can cheat, that being with Katy. Yet EVERY encounter is optional. Talking isn't cheating. Hell, you can't even argue that it's emotional cheating in the present timeline.
Three years have passed and you and Julia are together in the present timeline. You go back on a vacation to decide whether you can move on and marry Julia or if you can't let go of the past.
To the dev - I'd argue there are two big problems with this format. First, we currently have 100x more time in the past timeline, meaning we really don't have as strong of a connection with Julia as we do the other LI's. Meaning Julia is inevitably going to less important to the player. Second, as sisco pointed out, we're being given the opportunity to cheat on Julia long before we know what actually transpired in the past. It doesn't really fit the story you're telling. How badly did things really end 3 years ago that the relationship(s) were irredeemable? With Katy, the relationship could end due to you cheating shortly after you cheat on Julia with Katy. Why would she take you back when she knows you're cheating again?