Male lead is substitute for the guy female lead is in love with

The male and female lead are together, but he's just a substitute for a guy that the female lead is in love with. Eventually, though her feelings for the male lead turn genuine after realizing what she's put him through and that he's always been there for her. She rejects the guy and gets together with the male lead for real.

 AH:

Can you explain a bit more? Are you looking for dramas where the FL is using the ML as an emotional substitute for herself while she's in love with someone else, where she's using the ML as a substitute for the guy she loves in order to achieve some kind of goal (the guy she's in love with has a role to play and she needed a replacement for some reason), where she's using the ML to make the guy she loves jealous, or where the ML is pretending to be the guy she's in love with and she finds out?

Are you looking for something similar to a particular drama?

I'd take emotional substitute to alleviate the loneliness or she's using the male lead to make the other guy jealous. Like, if its emotional substitute, the ML is aware of her feelings for the other guy, but loves her and stays with her. So he knows he's a substitute. If she's using him, then he doesn't know he's being used.

 jak:

I'd take emotional substitute to alleviate the loneliness or she's using the male lead to make the other guy jealous. Like, if its emotional substitute, the ML is aware of her feelings for the other guy, but loves her and stays with her. So he knows he's a substitute. If she's using him, then he doesn't know he's being used.

This kind of remindes me of BIG, with Gong Yoo. I haven't watched it, so I don't know if its a good drama or not though.

 AH:

In Sound of the Desert the ML likes + pursues the FL from the get-go, but she loves the SL (even though she also has a friendly relationship with the ML / cares about him). The SL rejects her and she leaves the city. The ML tracks her down and eventually they get together when she's feeling particularly lonely and they both drink a lot and have a conversation about how they look out for and care for each other. She agrees to marry him and her feelings for him grow deeper over time. It's not my favourite start to a relationship, but the ML was definitely always there for her and they become a pretty epic couple IMO. 

Happy or sad ending?

 AH:

One of the happiest endings I've seen for a Chinese historical drama. The the main characters all live. The SL kind of gets the short end of the stick, but he lives, and the leads get to ride off into the sunset together with their kid. 

Good to know. I'll check it out.

I think Kuzu no honkai is EXACTLY what you are looking for. But it's not just the male lead who is a substitute, he also uses her in the same way.

Yeah, I know, it wasn't a very good drama imo. I didn't know you've already watched it though, it was not on your completed dramas list.