Im pretty sure its just downright homophobia. That and making the fact that MC is gay a burden that they themselves are facing so they are projecting it out on him. Which I do like that the story is touching upon because there are irl people who are like this. Which makes MC and MLs mutual healing all the more beautiful.
The translation is rough but they mentioned mc's dad not having enough money to basically help him avoid going to the military and in chapter 1 his ex told him not to enlist in the military because his dad agreed to help so I'm assuming he probably had an argument with his dad before or after and made his dad feel bad because he didn't have the means to help him and so he tried to invest his money to maybe be able to help him but ended up getting scammed whereas he might not have wanted to invest if not for mc. I think both his family and himself probably both did things to sour their relationship but I would hope they can look at things from the others perspective and forgive each other. And again this is how I interpreted the situation.
Base on the comments that i've read, i kinda connect the dots. So the mc doesn't want to go to military and maybe he begged his father to help him about it and it cost a lot.. that might also be the reason they were bankrupt beside his friend who scammed him.. even all those effort the mc left his family thinking that his family didn't accept him as gay which is wrong maybe they're just confused but they still care.. so back to the sis, the sis was mad bec mc left them that his bro is selfish left them behind.. so yeah the guilt he felt kinda valid.. he somewhat the reason why their family got in that situation.. the explanation provided in manhwa was too vague or too messy that's why it's so confusing. without checking the comments you'll really get lost
I’m clearing up the misunderstanding. I don’t know if it wasn’t mentioned in the manhwa but in the novel, he didn’t beg his dad to stop him from going to the military. He willingly goes to the military to avoid his ex. The reason his dad felt that way and tried to g et money to get me off military service was because they had an argument and MC said something along the lines of “(insert ex boyfriends’ name) dad is willing to help his random friend out of military service and what can you do for me?” That’s why his dad got sad about it.

Why is everyone in this story acting as if MC is guilty for being forced to come out? I don’t get why the sister’s angry, I don’t understand why he is at fault. Someone explain?