Jackie is dating Misty and there are other reasons why he's also not an option. Also, I don't think you miss out on content other than the romance itself by skipping the romances from what I've read.
I've had a few of the minor side quests spin into larger quests but still nothing like the more fleshed out quests. I've managed to fail a few quests now, one was time gated which I didn't think was a thing in this game, but I reloaded and completed it because I like the character.