You're in a pretty dangerous situation, not physical danger (well maybe), but I think you get what I mean. You are engaged to someone, yet have feelings for other men and not only that but you are getting to know these other men, probably on a level that is beyond "just friendship"...Have you gone to pre-marital counseling? If not, ask your boyfriend if he would be willing to go with you. You really gotta re-think marrying someone when you are so disconnected from one another. If he isn't willing to put God first and keeps putting it off NOW, he's probably not going to change later when you get married, although I'm not saying people don't change. Have you thought about spending some time apart and getting closer to God to see where He leads? Maybe that is the best thing for you to do right now. If you want to put God first, put this relationship on the back burner and seek God and His will for your life.
About you talking to the other guy on the phone, i'm sorry but I don't blame your boyfriend for getting jealous! He probably can sense that there are some feelings going on between you and this other guy. You BOTH need to work on this relationship by making some tough decisions about whether it should continue, be put on hold for awhile, or not continue. If he is not willing to work on the relationship and put God first, then he's not the one for you. Actions speak louder than words, so just saying he will work on it is not enough, and vice versa for you. Just remember that if you do break up, or even if you don't, God is always there as a Father, Friend, Counselor, and Savior!! Turn to Him for guidance. It's not easy, you likely won't get an answer right this minute or this week, maybe not this month...patience is the key.
Another piece of advice, and I say this because I know it's true in my own life, before you develop such a deep relationship or perhaps during, get to know who you are! What are your core beliefs? What things do you need to change? Have you had opportunities to be independent? Where do you see your life headed? It's really good to know you and who you are before you get to know someone else so intimately, which engagement is definitely a deep relationship.