It would be very difficult and long explanation, it is a quite complex topic... Try to see it from the point of view of a girl, any girl.
What does the girl want? She wants a man, someone who she can rely upon and depend on, someone who is a strong and mature person, someone who can make decisions under pressure. Someone who can see her as a sexual creature who loves sex, someone who she can have fun with, talk to easily... Someone who is emotionally stable, independent, not needy or clingy, someone who knows what he wants...
So this kind of man knows what he wants in his life. He has his mind and his opinions, and these don't change because of anyone - not because of other men, not because of any women. He keeps his views no matter what, he doesn't need anyone's approval, he doesn't seek anyones agreement. He doesn't need her approval, he doesn't need her to agree with him either. He doesn't need anyone to love him. He doesn't need his mama to love him nor his GF to love him. He is simply independent, emotionally stable, mature. No longer he is a boy, he is a man.
Women are very sensitive, their brain is setup differently than men's brain. They know the difference between boys and men, they can just feel it. Boys are immature, clingy and needy. Boys need a lot of attention and affection. Boys require love and they usually get it from mothers, if not they cry. If they are immature, and I am not talking about age only, they will require a lot of love and affection from girlfriends too. They will be clingy and needy, they will want all of the love for themself only because they are still those little boys...
What happens to this sexy girl when she meets a boy like this? Her interest in him will drop fast. She will refuse to be his mama. She doesn't want to be his mama, she only wants to be mama for his children. She doesn't want him to be dependent on her. She doesn't want to be the one who he needs affection and love from. She doesn't want to see him cry on her shoulders. So if he can't provide some traits of a man she will dump him very fast...
You can't convince any girl to love you, it is not a question of conviction. You can force her to be with you, through religion or otherwise, but that is not a love. What you can do is to become more attractive, more independent, more mature and stronger, less needy and less clingy... You can only OFFER her your love by becoming a bigger and more independent man, but even then you can never convince her to love you...