The premise could stay the same, except that instead of the shitty excuse, it could've been a genuine accident instead. Like the twin brother understood the MC and ML had mutual feelings and wanted to support them, but whoops, accidental heat. The pregnancy then forces the twin and ml to stay together, they both feel responsible and guilty, staying only for their kid. However, the accidental heat and pregnancy, suddenly being married to someone he doesn't love/doesn't love him back, and also being with someone he knows his brother loves/that loves his brother leads the twin to run away out of guilt and anxiety. The MC and ml live together the same while trying to find the twin, and when they find him they have a discussion about what happened. Through that, the ml and MC find out their mutual feelings while resolving the awkward situation regarding the child's true parentage
The premise could stay the same, except that instead of the shitty excuse, it could've been a genuine accident instead. Like the twin brother understood the MC and ML had mutual feelings and wanted to support them, but whoops, accidental heat. The pregnancy then forces the twin and ml to stay together, they both feel responsible and guilty, staying only for their kid. However, the accidental heat and pregnancy, suddenly being married to someone he doesn't love/doesn't love him back, and also being with someone he knows his brother loves/that loves his brother leads the twin to run away out of guilt and anxiety. The MC and ml live together the same while trying to find the twin, and when they find him they have a discussion about what happened. Through that, the ml and MC find out their mutual feelings while resolving the awkward situation regarding the child's true parentage