What is the ruling on someone who committed zina while being muhsan, without penetration, and his intention was marriage? And how can he repent?

What you did is forbidden and is a type of adultery that necessitates repentance by feeling remorse and resolving not to return to it. Sincere repentance erases sins by the will of Allah. You must conceal yourself and not speak about the matter, and beware of being alone with a non-mahram woman, for Satan is the third of them.