The term "most two-timing" refers to someone who is notorious for cheating on their partner or being disloyal. The antonyms for this phrase would be faithful, loyal, committed, devoted, trustworthy, and dependable. These terms describe someone who is committed to their relationship and would never cheat on their significant other. A person who is described as faithful, for example, is someone who is dedicated to their partner and works hard to maintain the trust and honesty in the relationship. By contrast, someone who is most two-timing is known for their deception and dishonesty. Therefore, the opposite of most two-timing is someone who is honest, dependable, and loyal in their relationship.