Can the questioner be accused of deviancy and homosexuality after he touched his cousin’s penis and semen was discharged during their sleep, and given the cousin’s angry reaction to that?

You must repent to Allah for what happened, because it is a precursor to sodomy and deviancy, which is forbidden by the consensus of Muslims, as stated by Sheikh al-Islam Ibn Taymiyyah. The real problem lies in a person's standing with Allah. Ibn al-Qayyim advises that sincere repentance (tawbah nasuḥ) should include three things: encompassing and covering all sins, a sincere and unwavering resolve to repent, and purifying it from impurities and defects so that it is purely for the sake of Allah, out of fear and hope for what He possesses. The cousin should have concealed the matter and not exposed his friend.