RUN for your life!!!!!!
Run from this guy and this relationship for the sake of your future children and your grandchildren.
I do not care one jot if this guy calls himself a 'Christian' because by his behaviour he is in fact NOT one. He is not only a hypocrite but also a pervert and a manipulator.
Yes you are in this sin with him, but his behaviour is appalling even more by the fact that he is asking you to participate in cybersex and sending him naked photos of yourself knowing full well that this is wrong biblically, so there is no way this guy can claim any spiritual or moral ignorance. Please STOP enabling him immediately. If he is away often and asking for naked photos I would then make an educated guess that he is also looking at some form of pornography (which he might feel guilty about and therefore feel justified by asking for 'porn' containing images of you).
Not only should you break up with him, but you should alert Pastoral Elders or a trusted pastor over the sin you share and repent asap and also what he is asking of you. In order to obtain the honour of serving in church with the goal of being in some form of leadership position (which all men are in anyway), men need to meet the character qualities of 1 Timothy 3:
Now the overseer is to be above reproach, faithful to his wife, temperate, self-controlled, respectable, hospitable, able to teach, 3 not given to drunkenness, not violent but gentle, not quarrelsome, not a lover of money. 4 He must manage his own family well and see that his children obey him, and he must do so in a manner worthy of full[ respect. 5 (If anyone does not know how to manage his own family, how can he take care of God’s church?) 6 He must not be a recent convert, or he may become conceited and fall under the same judgment as the devil. 7 He must also have a good reputation with outsiders, so that he will not fall into disgrace and into the devil’s trap. 8 In the same way, deacons are to be worthy of respect, sincere, not indulging in much wine, and not pursuing dishonest gain. 9 They must keep hold of the deep truths of the faith with a clear conscience. 10 They must first be tested; and then if there is nothing against them, let them serve as deacons.
This is the standard of all male leaders, and since in Hebrews 13:7 tells church members to imitate their leaders, this list of behaviour is held for all men in the church, and your boyfriend fails miserably at this test. He has already cheated his future wife (which you do not hold title to and might never), hes preaching a false doctrine with his outward behaviour when his heart is thinking evil, and he is sexually abusing you by expecting intimate privileges of marriage without having earnt anything by being faithful to Gods standards.
If you marry him, your life will not improve but worsen. And by seeking marriage just to justify sexual sin is the worlds worst proposal and you should be deeply insulted. Break up with him and continue your education and get some counselling re your sin from someone trusted in your church. And above all else, ask the Holy Spirit for conviction on your behaviour so you can effectively pull the plug on this relationship and sin.
fighting!!!