For instance: Deadpool. I actually thought the relationship between Wade and Vanessa was pretty intriguing. It was refreshingly sex positive - instead of building up to one big act of romantic, passionate lovemaking they just hop into bed together, and they actually reveal character through that epic sex montage. It isn't just filler, you'll miss valuable character details if you skip the sex scenes. The whole "she'll hate me because I'm ugly now" plot was a bit dumb, but overall I think the acting and writing saved it.
Any other examples of movies with a romantic subplot that was actually well done?