Yibum v’Chalitzah 5:2

Maamar (a yavam’s statement that he intends to marry the yevama) does not fully complete marriage with her, nor does it make her a married woman in the ultimate sense, but a man who has performed maamar must give the woman a get (if he decides not to perform yibum after all); in order for her to marry someone else, she would need to perform chalitzah.

Yibum v’Chalitzah 5:3

Accordingly, if a yavam makes a statement of maamar to his yevama but he doesn’t want to consummate the relationship, he must write her a get because she was betrothed to him, and they must perform chalitzah for her to be able to marry someone else. This is because a yevama is not permitted to marry anyone else without first performing yibum or chalitzah. Giving her a get disqualifies her for yibum but it does not suffice to allow her to marry anyone else. Maamar doesn’t complete marriage the way that marital relations do.