Ok so I read the chapters on manga pl*net & spoilers for anyone who wants to know!

So there's 2 volumes, also sorry it's kinda messy I typed this while I read
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The omega mc agrees to become fake bond partners with the alpha mc and the alpha's grandmother doesn't seem happy about it because he's an "omega past his prime." Both mc get giddy thinking about their fake relationships and have a date planned.
The alpha mc his grandmother is actually his stepmother, but he was always told to call her grandmother. His father is now living abroad with the alpha mc's mom. The BIL has an alpha supremacist father who I think is the chair or something for the hospital. He tells the BIL to marry even though his wife is pregnant because it is not an alpha's role to be a parent or raise children. I guess in their society only alphas can get married to multiple people.
The BIL has feelings for the omega mc.
The alpha mc feels that omegas should only have one pair so that there is mutual respect and less omegas in pain because they're only married to have kids.

So the 2 mc go on a date and the alpha is very attentive which the omega appreciates and they have a cute day together. They go to alpha mc house and have tea but then he says he only wants to be with the omega mc and doesn't need to smell other pheromones. Then it almost goes too far and the alpha's mom barges in (he's a male) and that leads them to have to formally introduce omega mc to the family as the alpha's first bond mate. All the alpha mc's sisters are there including their partners. He has four older sisters, but he's the only one with a different parent and was the only one who was given special treatment when they were young because he's a male and an alpha. 3/4 sister's bullied him and the only one he's close to is the one BIL is married to. So of sisters the oldest is an alpha, 2 omegas, and 1 is a beta.

The alpha's dad is against the mc alpha being with and older omega who they don't know if he can have kids. The alpha mc says he only wants to have one bonded partner out of love like how his parents are. The alpha dad twists the parents story slightly to say it wasn't out of love they got married, but because their families benefitted from it and alpha mc runs away. The alpha mc's mom comes and says that he told it wrong and he would've never married him if he didn't love him and they both knew that.

So outside is the omega mc and BIL and alpha mc is listening to their conversation and they did sleep together during a heat or rut. BIL said he could've force omega mc to let him bite his nape and omega mc is getting scared by this conversation as BIL has him cornered. Alpha mc releases pheromones to get BIL off and away from omega mc. They leave and alpha mc tries to confess but omega mc doesn't let him.

BIL and sister actually have a decent relationship and actually wants to make her happy. After they return home form the family house BIL tells sister that the relationship between the 2 mc is all a lie and omega is just going along with it. After hearing this sister tells BIL that she went into this marriage knowing BIL would bond with other omegas but tells him she's fine with that, but asks him to promise to never bond with omega mc and to give up on him, BIL is shocked.

Now at the hospital omega mc is talking with his friend and omega mc says he's going on heat leave soon and will be spending it alone. Then comes a surgeon who is married to the friend and they have a daughter together. He sees omega mc will be spending heat alone and talks about BIL. He says it's a shame the sister got pregnant while the omega MC and BIL were still together. Omega mc says he chose to live that life so he should dedicate himself to his wife not me basically. Then it shows BIL thinking about what his wife said and says he has no choice but to agree.

So the next part kinda confused me but it's a flashback with omega mc and a lawyer from BIL's family asking him if he prepared a dowry (which I thought was money prepared by the wife's family to present to the husband), but they say it's a contract basically ensuring no divorce even if no kids a re born. Since the BIL is set to marry the sister the omega mc would have to sign some form of bond contract and it would be inconvenient if omega mc and BIL bonded so they offer him a check (SORRY it's confusing I was too). Omega mc accepts the check and breaks up with BIL since he is starting his practice, he was about to rip it up but started crying that he chose financial security over love. Then BIL goes to omega mc house (he's in heat) and they have sex and omega mc said they continued their relationship even though BIL was married. WOAH, ok, so omega mc hears BIL talking to someone about his wife being pregnant and he runs away and is in pain so the surgeon takes him to a different hospital where he finds out not only was he pregnant, but he also lost the baby. The dr tells omega mc the chances of him getting pregnant again is very low because he is a male omega. Then he wakes up and is back in the present time and lusts over alpha mc during his heat.

Alpha MC is worried since omega mc hasn't contacted him so he calls him and goes to his place but the omega mc doesn't let him in since omegas and alphas can't resist the urges of heat. They talk over FaceTime outside and the alpha mc mouths the words "I love you" and they continue talking a little and hang up. The omega mc decides that their fake relationship can't continue since he isn't a good omega who can have kids. The alpha MC goes home and researches omega heats and feels it's unfair that they only talk about alphas and how omegas will be fined if they go out in public and tempt alphas. He is sad and feels there's no way omega mc is ok.

OK so the alpha mc family does background checks on people and the omega mc came up when they did one on BIL but just dismissed it since their relationship wasn't acknowledged. Since they think he is serious about alpha mc they look into his file and see his mom died during childbirth and his father gave him him so he was raised in foster care. The grandmother is the one reading the report and also discovers the omega mc was pregnant but never gave birth and concluded that he was pregnant with BIL baby. So the grandmother says once omegas get pregnant by one alpha they can never get pregnant by another alpha regardless if they were bonded or not. So basically the 2 mc can't bond. Also she wasn't evil about receiving the information she just felt sorry for the 2 mc and said in her mind to the alpha mc that's why you shouldn't fall in love.

So now the sister goes into labor and BIL at first rejects her call but picks up when he finds out it's and emergency and goes to inform two mc who are also at the hospital. Alpha mc gets mad that BIL is so dismissive of his wife as she could be in danger and he should've gone to go pick her up. They keep arguing in the hallway until the grandmother shows up to stop their fighting. She thinks they're fighting over omega mc and says it's not up to them who he chooses, it's entirely up to omega mc who he wants to forma bond with. Sister gives birth to baby girl and omega thinks he wants to form a bond with alpha mc. OK then it kinda ends there. There's a brief mini story with the surgeon and his male omega wife

OK so TLDR - BIL and omega MC were in a relationship even when he was married to the sister. Sister knew about their relationship and forbids him from bonding with him but is fine if he bonds with anyone else since that's what alpha and omega marriages are like in this world. Omega MC had a miscarriage in the past with BIL and can no longer have kids. Omega mc and alpha mc kinda end up together but they don't go into a lot of detail or get married or anything.

Again sorry it's messy! I'm not really satisfied with the ending, but what could be done.