Least favorite romance:
It's between Bruce x Natasha or Steve x Sharon. Both of them have huge issues, so it's kinda hard to choose.
Bruce x Natasha was a horrible relationship because it showed up out of nowhere. It had no development and was completely dropped in Infinity War (except for that one scene where the ex-vengers found out that Bruce returned) In Avengers and Captain America: The Winter Soldier, Clint x Natasha was supposed to be a thing, but then stupid Age of Ultron happened and that all flew out the window. (I think you can tell I ship Clint x, Nat. I also ship Nat x Bucky, Nat x Daisy, Nat x Maria, Nat x Carol and Nat x Wanda. I'll ship a lot of people with Nat, but Bruce is not one of them)
Steve x Sharon was a horrible relationship because Steve kissed Peggy, then kissed her niece. Then, he goes back in time to go fuck his girlfriend's aunt. Do you see the issue? Pick one Steve! You're not Zeus, you can't go around fucking everyone.