Is what the questioner did, such as contracting the pelvic muscles or touching the breasts with the feeling of lust and the emission of a clear, viscous fluid, considered forbidden masturbation, and does it necessitate Ghusl, and are there special supplications to reduce excessive lust?

Praise be to Allah who has bestowed upon you repentance from masturbation. You must remain steadfast in this. What occurred, touching the breast with the intention of pleasure, is a form of masturbation. The fluid that was discharged from you is most likely madhy (pre-seminal fluid), which necessitates ablution (wudu') and cleansing whatever it touched. As for mere fantasies, there is no accountability for them unless they lead to an action. However, beware of indulging in them, as they are a gateway to temptation (fitnah) and corruption. Ibn al-Qayyim said that the root of corruption stems from neglecting thoughts. Beware of the devil's despair and his whisperings, seek Allah's help, and supplicate frequently. Your fear of hypocrisy is a sign of sincerity.