Antonyms for the phrase "mixing it with" could be "separating from," "isolating," or "keeping apart." When we mix things, we combine or blend them together to make something new or different. However, in some cases, it may be advantageous or necessary to keep things separate. For example, separating incompatible chemicals might prevent a dangerous reaction from occurring. Similarly, isolating contaminated substances from clean ones helps to maintain hygiene and safety. Keeping things apart might also apply to social situations, such as avoiding certain individuals in a group or not mixing personal and professional relationships. Ultimately, the opposite of mixing things together is to keep them separate or apart.