Should the husband confess to his wife if he cheated on her?

Help me, so, A very young man and a very young woman came from different countries to study in the Soviet Union, meet each other. They love each other and lived together for years. They couldn't legally marry because as foreigners in the USSR, they would have to fly back and forth to their own countries,... show more Help me, so,

A very young man and a very young woman came from different countries to study in the Soviet Union, meet each other.
They love each other and lived together for years. They couldn't legally marry because as foreigners in the USSR, they would have to fly back and forth to their own countries, and as students they don't have the money to do that. And the woman's family want her to marry someone from her own country.
Both the man and the woman are very patriotic by the way.
So after a few years together, the very young woman becomes a young woman and decided that there was no future, she could never leave her own country and all her family to live in Mid-East with her boyfriend. So the young woman rejects the young man and flew from the USSR to Mexico and USA to finish university.
(An important point is that they broke up NOT because they didn't love each other anymore.)
After a while the young man thinks she has left for good, finishes his studies, marries a local woman and has a baby daughter. Very soon after this, the young woman still loves the man and came back to see him, not expecting him to be married I think.
The young woman was probably sad, and she asked to carry that man's baby. The MARRIED young man (with a 1-year-old daughter) agreed to the woman's decision and they expect a baby daughter...(so the girl wasn't an accident or anything).
They both stayed in the same city and the father would visit the daughter and the gf 1, 2 times a month...
After a few years, the woman takes the girl and move back to her country and got married. The man also took his family back to his own country.

The daughter grows up with her mom and step-dad never knowing her father. Her step-father became her legal father who basically never even notices the girl. The girl becomes a moody teenager with serious emotional problems. She didn't like the step-father a bit and made problems until the woman/mother contacted the father and ask him to see the girl. The girl meets the man again after 10 years separated and immediately adores him. I think the father loves her too... But if anyone knows about her then the father would have problems for committing adultery obviously.
So the girl will rarely ever see him, and has to stay a secret and can rarely phone him.
The girl wants to think that cause she loves him so much she wouldn't want him to have any problems with his life and family, but deep down she also wants to be known so that she could be/talk with the father always. That is probably a selfish thought...

but what is the RIGHT, MORAL thing for the father and the daughter to do? Because the daughter apparently really wants to be with him, except she doesn't want problems for him either...Is it immoral (for the girl) to secretly want the father to come clean to his family so that she could know her father and her siblings? What is the right thing for the father to do?
Update: Thanks for even reading this! I tried to make it short already, I cut out tons of details but it still ends up long :( Poor daddy, it wasn't his decision!!!! Aw I miss him :(
Update 2: oh and did I mention the married man and the married woman still are VERY close...though they shouldn't be.
Update 3: That's true Kate!!! :( Sometimes I wish things were different.
Update 4: wow ~ your answers are touching enough for tears! Thanks. I think I will come to a conclusion that ME the girl, only 1 person hurt ... is better than having his HUGE family, (whom I don't know but love) hurt. I will tell him that if I could go to Lebanon :)
Update 5: Thanks LBebe!!!!! I cannot possibly choose a best answer for this question. But I am printing it out and keeping it, maybe until the day things work out...somehow, when one of us dies or something like that.
Update 6: I am also VERY very glad that I spent the time to write this.
Update 7: I forgot to mention. I'm actually supportive of his cheating - cause if he didn't... I'd never exist, at all.
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