Of course, it is necessary to behave very cautiously and pedagogically. Youthful maximalism and first love turn children into capricious and stubborn, therefore prohibitions here will not be helped in any way. If you just make a girl not communicate with her lover, she will hate you. Of course, this feeling is temporary, and after growing up, your daughter will understand everything. But, now, she will consider that you take away from her the happiness and love of all life. Even if you close her houses and put in total control, she will be able to find a way to escape, and to spite you, she will do even more stupid things than she could if you did otherwise.
Therefore, try to become her friend. At this age, adolescents trust much more to their friends than their parents. She must understand that you will not condemn her, forbid and teach. In addition, do not tell all friends and acquaintances that my daughter fell in love with an adult guy. The girl will be offended at you, knowing that those feelings, which at this age seem to be the purest and brightest, have become public.
The best way out of this situation will be constant communication with the daughter of a tete-a-tete. Just never press it and do not try to extract information. Let her know that she can only say what she wants and then when she wants to. Of course, the girl will not immediately trust you, especially if earlier you already had conflicts on such grounds. But, if you choose a friendly model of behavior, soon the child will understand that you can trust everything and start talking about your problems. This information will help you decide how best to proceed.
Of course, in most cases, such relationships do not lead to anything good, because an adult guy sooner or later just gets tired of a child who is your daughter. But there are times when her lover really turns out to be an intelligent and serious young man who loves a girl. To understand this, ask your daughter to invite him to visit. But in any case, do not insist and persuade. Act like it's almost not important to you. If the guy refuses the invitation, this fully confirms his frivolity. Acquaintance with the mother of the girl, basically, frightens only those who do not want to be able to make claims to him close girls.
In a case where he still agrees, try to evaluate him, and his attitude. Of course, each mother wants the perfect pair for her child, but still it is worth thinking adequately and rationally.
In communication with a young man, try not to be too intrusive and in no way say what your daughter thinks might offend or compromise her or the guy. Even if at first glance you realized that this is a slippery type, keep on behaving naturally and friendly. You really need a girl to listen to you, so you must keep the status of her girlfriend.
If the young man does behave decently, then, perhaps, it is better to give him a chance. Just try, as far as possible, to monitor the situation. It may well be that this young man will be able to make your child happy. So do not let yourself be prejudiced. Always be objective.
But what about when you realized that a young man is not at all suitable for your daughter? In this case, you must convince her of this. But do not try to bring it to clean water, adjusting the compromising situation. It is unlikely that the girl will believe you. Most likely, she will say that you deliberately do this and find a thousand excuses for your boyfriend, even in what can not be justified, in principle.
Persuasion is the only way to influence the daughter's decision. You need to talk to her constantly, discuss the guy the way she does it to her friends. In her speech, it will be necessary to skip a note of discontent with some situations. That's what we need to start with. By accident, ask about what she does not like, try to simulate various options for why this happens. But never leave the last word for yourself. Let your daughter have an opportunity to comprehend everything, and not try to convince you. Tell her instructive stories about such situations, but try to make sure that everything does not look like moralizing. The girl should feel that you are communicating on an equal footing and will never force her to give up her beloved. All its solutions must be independent. At least she should think like that. Have patience, behave with restraint and tact. Never show your true attitude towards a guy. You are wiser than your daughter and her young man, who surrounds the girl with the most primitive methods, several times. So use your privileges. Always act according to the situation. Your daughter must consciously think that you are her friend, but at the same time subconsciously feel an unshakable authority in you. If you can achieve this, then the words you said will be for her laws, even if the girl does not realize this.
Of course, you need to get rid of unhealthy relationships as quickly as possible, but in cases with adolescents, haste can aggravate everything. So be patient and try to keep abreast of everything that happens to your child. Tell yourself: "This is my daughter, for her sake, I'm ready even to wait, to suffer - just not to hurt!". If you do not break and do not go to extreme measures of education, in the end, everything you said will be meaningful, and the daughter herself will make the right choice. And then you can again sleep soundly and do not worry that someone will be able to offend your girl and break her heart. After all, in the end, even if the baby (and your daughter will always be your baby) fell in love with an adult guy - it's not the end of the world!