I just don't understand "not being ABLE to abstain" from sex. Is there nothing else to bring you to close? Sex is the most intimate thing to can do, the most private, intimate, personal thing you can give another and that is why it is a GIFT of God to be given to the person you are betrothed to, under the covenant from God. You can and you should stop. You just don't want to. What will be special about your life together once your married if your acting married already? No, I don't think you will 'go to hell" because of this, because God forgives, but you won't experience all that God has for you here on earth if you blatantly disobey, knowing you are disobeying, admitting you intend to keep on disobeying. Remember, some call the name of the Lord and yet He says I do not know you.
Professing your love of God has to be backed up with what you do.
Think about a spouse who says he loves his wife but stays out all night with the guys when his wife has asked him not to. He continues to say he loves her but continues to go against her wishes, every weekend. Tells her I love you, honey, but I just can't keep from getting in the car, driving there, staying there till the sun comes up, etc. How much love does this really show? No, the spouse wants to play poker more than he wants to please his wife. She may not divorce him but he won't be having the loving, intimate home life he could have.
Forgive me if these sounds like a rant. May God bless you both with strength. I am praying for you.