They are both part of the same trilogy . Similar vibes very different storylines. SH has a more melodrama feel. The main leads in H&LF are in the opening episode of SH on their honeymoon.
The couple from Happy & Love Forever play a supporting part in the first episode of Sunny Happiness. Also, its your basic romantic comedy too!
They are extremely family focused and they are also in a contract marriage for the sake of a child. The female lead marrys to a rich family. It really gives me the same feeling and this drama also made me cry.
Both dramas involve an accidental pregnancy and contract marriage that brought the leads closer. The female lead in sunshine happiness wanted to save an orphanage and the female lead in fated to love you wanted to save a soap factory and her hometown. Both female leads are both caring individuals who puts other's needs and feeling first. This traits endeared them to their respective male leads.