Ok first your best male friend in an ideal world would first be the man you are planning on marrying and having a life together with.
My bet is in any case that the feelings your "best friend", who was always there for you, finally expressed had been existing for many years in his heart.
Sorry the man is not your "friend" he is someone who is in love with you and for everyone good I suggest you keep the relationship to a few messages on facebook at least until he is in a long term and happy relationship himself with some other woman.
Oh if you would like to get an idea of the emotional turmoil he is likely to be in try putting yourself in his place in that you been in love with a male friend for years and when after he broke up a relationship you and him had a short sexual relationship and you told him you was in love with him.
His reaction to that was to break contact with you and then to get engage to another woman.
It going to take time for all this to settle out.