What happens if a lesbian sees annother woman only to find out mabe years later that the woman is in fact a guy how does the lesbian cope with that situation?

If I understand correctly, you're asking how a lesbian woman would react to discovering that a woman she had had a relationship with had actually been a man. The answer is obvious: it would entirely depend on the woman in question, her attitudes about sex, gender, and of course the other person; the circumstances (was it active deceit? was the person experiencing confusion about their gender? etc). Or perhaps you mean that years later she discovered an ex was transgendered and had since become a man in body and gender presentation. I'd like to believe that most lesbian women would deal with such news by feeling happy for them for dealing with something that must have caused a fair amount of pain in their life, but of course even some lesbians can be anti-trans.
There's no particular way that lesbian women would deal with this situation that's different from how anyone else might.