Never Forget Your Enemy

After a car accident, Ki Ha Neul wakes up at age 29 with only the memories of his 19-year-old self, losing an entire decade of his life. The biggest shock comes when he learns that during those missing years, he was in a seven-year relationship with his lifelong rival, Yeo Sae Byeok.

While photos, messages, and even his own instincts suggest they were deeply in love, Ha Neul remembers him only as the enemy who overshadowed him throughout childhood. As fragments of memory slowly return, he begins to suspect that their relationship ended for a reason and that Sae Byeok may be hiding the truth.

From the synopsis, both series have enemies to lovers vibes.
Both are BLs. Both are from Thailand though Never Forget Your Enemy is made up of Korean cast.

Both MCs forget their past including that they are in a relationship. The MLs try to make the other remember or fall in love with them again.

The similarity in both Never Forget Your Enemy and Secret Lover is that the main couples are childhood friends that turn to lovers. Also, one of the boys secretly keeps girls from approaching his friend by dating them. It started as a requited love then they became boyfriends in their later years after high school.