Is embracing the blanket (haram) when remembering fondling one's fiancée, leading to ejaculation, considered masturbation and forbidden?

Masturbation by any means to release semen, other than through interaction with one's wife or a slave woman, is forbidden and requires repentance. This is indicated by the generality of Allah's saying: "And those who guard their private parts Except from their wives or those their right hands possess, for indeed, they are not to be blamed – But whoever seeks beyond that, then those are the transgressors."

If a valid Islamic marriage contract has been performed with a woman, then it is permissible to be alone with her and enjoy her company. However, if it is merely an engagement and a preliminary agreement, she remains a stranger (non-mahram), and it is not permissible to touch her or be alone with her. One must repent from any forbidden acts committed and resolve not to return to them except after the marriage contract is concluded.