Since I know neither you, nor your two friends it is impossible for me to give an opinion as to which person you should have a relationship with. But I will give you some general advice:
1) PRAY SOMEMORE!!!! I know you have been praying, but if God hasn't given you an answer it's either because you haven't been listening out for his answer, or God's waiting for you to trust him a little bit more with this decision.
2) As CoffeeCat wisely said you may want to back away a few steps, take a deep breath and focus on God. Considering you were (and sort of still are) in a relationship with Sam in order to recieve something from him rather than give, it would be a good idea to submit yourself afresh to God and recieve what you were recieving from Sam, instead from God. Once you are fully dependant upon God, you can then be in a selfless relationship of your choosing. As I am not a woman this advice may not be perfectly suited to you, but this is the advice I would give to a man in a similar situation.
3) PRAY SOMEMORE!!!! (seriously it works)
He's charging into hell and bringing heaven with him!- Rob Bell
"So you are no longer a slave, but a son; and since you are a son, God has made you also an heir" - Paul - Galations 4:7