My Best friend's boyfriend in love with me

Hello,

I have a childhood friend of mine, who is committed with a boy of our class. Actually I helped the boy to confess his love for my friend and propose her as i knew my friend, she also used to like him. In a way, I was the reason/medium of their relationship.

After this incidence that guy became one of my very good friend and whenever my friend got angry i helped that guy and told him how to convince her and make her happy. And from time to time I used to give him suggestions about what my friend likes or dislikes. Their relationship was going very smoothly and i was the happiest person seeing them together.

But because of spending a lot of time together that guy started developing feelings for me. Now he says he only likes my friend but actually loves me and want me to marry him.

I feel like i am betraying my friend not telling her about this situation. But if i tell her she will not only break up with her bf but she might end our lovely friendship. what should i do?

That's a classic issue, but you have not mentioned anywhere what you feel about him ?
Do you like him or love him that you can marry him ?

Well, it's like he do cares a lot for me, he is sweet and smart but i have never seen him with the eye of a gf. for me he is just my friend a best and moreover my best friend's bf. she do loves him a lot and i feel guilty thinking about that guy as my bf. i don't know how much he mean it. all i know is he is from a very good family and is not a kind of cheat/playboy. he might be serious for me but i don't know what to do. he wants to marry me but all i think about is my best friend. my feeling is nothing in front of my best friend's feeling. i cannot cheat my friend. she is like my sister and no girl cheats her sister.

if he would not have been my best friend's bf i might consider the fact of him loving me. i might have though to marry him. i would have. but since my answer and acts affects my friends live directly i cannot think of anything