I've been reading this site and you give such meaningful advice to people, so I wanted to ask a question of my own: Is it possible to take a leap backwards after you feel like you and your boyfriend have gone too far physically? We haven't had any sexual contact, but I'm afraid that cuddling and kissing have come too fast, and I worry about the temptation either becoming even stronger or ruining the relationship.
You are right to be concerned. The nature of sin is to progress further and further. That is why Paul warned, "Now concerning the things of which you wrote to me: It is good for a man not to touch a woman" (I Corinthians 7:1). By "touch" he is meaning sexually arousing touch, and the reason is clear -- it leads to fornication (I Corinthians 7:2).
Can you step back after going too far? It should be clear that you can. Sin doesn't have to be repeated just because it was done in the past. That is why Christians are able to leave sin, even sexual sins, behind. "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God. And such were some of you. But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God" (I Corinthians 6:9-11).
While you haven't gone so far as fornication, it appears you are being tempted with passion. You two can step back from this, but you both have to be resolute about it. You are going to find it near impossible to resist temptation if one of you continues to press greater heights of sexual pleasure. You could say that how you two deal with this problem will tell you a lot about the other. If you are determined not to sin but he keeps fanning the flames of passion, it tells you what is more important to him. Perhaps he is not as good husband material as you had thought. But if he agrees and appreciates the boundaries being placed, then you've found yourself a good man.
"For this is the will of God, your sanctification: that you should abstain from sexual immorality; that each of you should know how to possess his own vessel in sanctification and honor, not in passion of lust, like the Gentiles who do not know God; that no one should take advantage of and defraud his brother in this matter, because the Lord is the avenger of all such, as we also forewarned you and testified. For God did not call us to uncleanness, but in holiness" (I Thessalonians 4:3-7).