The 12th house - the closed house, the house of solitude, immersion in oneself, in one's inner world. This is a difficult position for Venus. Feelings and emotions in the closed house... Of course, this is not an isolated person, he can be a socially active person. But his emotions are hidden from outsiders, from other people. This is only his personal business. He will not advertise them, expressing them on display.
Such a person may find it difficult to express his emotions, or there is an unconscious feeling that his feelings will not be perceived, his love will not be accepted.
Very often there is a feeling that love is something distant, unreal, cosmic, and therefore it is impossible to get it from one's partner. It is difficult to achieve harmony with a real partner. Hence love disappointments, may suffer for a long time in relationships. It was love, and now it is gone. And the person begins to look for love on the side.
But there may simply be love for an inaccessible person (married, abroad, and other reasons), just the impossibility of being together. But there are feelings, and the person suffers internally.
Tragic stories with a loved one are possible, but here there must be other indications in the card (one Venus in the 12th house is not enough in the card, we look at the connection of houses, aspects, rulers).
Sometimes a person just falls in love with unusual, mysterious people, not like everyone else, as they say "not of this world". Or a person finds love abroad, or simply far from home. And this is not necessarily bad.
Venus in the 12th house can also show hobbies that a person does not want to advertise. The main thing is that he likes it, it is his personal business. He loves to engage in an art form that is interesting to him, in this he sees some kind of kick, genuine interest, but he will not tell anyone about it. Maybe he is engaged in dancing, remember the movie "Let's Dance" with Richard Gere and Jennifer Lopez. He went in secret from his wife, but what a dance it was - sensual, passionate, in this he saw some kind of outlet. Or the same occultism, whatever, but he will not spread this topic.