There can be many reasons why a husband may lose interest in his marriage. Some possible reasons may include:

1. Lack of emotional connection: If a husband feels emotionally disconnected from his wife, he may lose interest in the marriage.

2. Lack of physical intimacy: A lack of physical intimacy or a lack of connection in the bedroom can also cause a husband to lose interest in his marriage.

3. Differences in values or goals: If a husband and wife have different values or goals, it can cause conflict and lead to a loss of interest in the marriage.

4. Infidelity: If a husband has cheated on his wife, it can cause a significant loss of trust and lead to a loss of interest in the marriage.

5. Stress and other external factors: Stress at work, financial issues, or other external factors can also contribute to a husband losing interest in his marriage.

To try to win a husband's interest back, it can be helpful to try to address the underlying issues that may be causing the loss of interest. This may involve seeking couples therapy, working on communication and intimacy, and finding ways to reconnect emotionally. It may also be helpful to take time to focus on individual needs and interests, and to make an effort to support each other's goals and dreams.