Antonyms for "becoming partners" would be ending a partnership, ending a relationship, terminating a business relationship, breaking up, or dissolving a partnership. All of these terms denote a separation or severance of ties rather than the creation of a new partnership. For instance, when a business is no longer profitable or the partners are at odds with one another, they may choose to dissolve the partnership. Alternatively, a couple may break up or end their relationship due to irreconcilable differences, allowing them to go their separate ways rather than continuing their partnership. Ultimately, antonyms for becoming partners involve ending or severing an existing relationship rather than forging a new one.