What is the most I can do sexually with my girlfriend before marriage? Can I engage in any act so long as it does not stimulate the genitals?
May I suggest you take a different approach and ask different questions? You mention marriage, so I infer you’re engaged to your girlfriend or on the threshold of engagement, correct? If not, then take this advice in light of how you would want your future wife—whoever that might be—to be treated by the men she dates before meeting you.
First off, to answer your initial question, it’s prudent to engage only in chaste hugging and kissing—brief kissing. Men are “microwaves” and women are “crockpots,” so don’t delude yourself into thinking you can avoid being sexually aroused by any type of passionate encounter with your girlfriend. Nothing wrong with being sexually attracted to a prospective spouse; you should be, in fact.
However, be sober in realizing that you can “heat up” quickly and therefore increasingly desire to engage in the marital act prematurely. We can easily compromise our consciences when we’re in the throes of passion.
But ask yourself this question: how can I best prepare to be a great husband? And how can I best witness to my girlfriend regarding what she should expect from a boyfriend and prospective husband?
Learn to cultivate the virtue of self-control now. You’ll need it in marriage, including at those times when you might desire conjugal intimacy with your spouse but for one legitimate reason or another you’ll have to exercise discipline and seek express love for your wife in non-conjugal ways.
Spend time with your girlfriend. Get to know each other well. Learn how to communicate well with her. Discern whether the two of you have the makings for a good marriage, which will involve much more than conjugal intimacy. And if you can love your wife in various non-conjugal ways, you won’t have to worry about conjugal intimacy. She’ll be more than disposed.
In general, honor your girlfriend. If you become engaged and get married, you’ll both be well-prepared for marriage. If not, then you will have given your girlfriend a great virtuous standard by which she can measure prospective husbands and quickly walk away from those who don’t measure up. That would be wonderful gift in our misguided culture today in which women are often asked to succumb to the premarital demands of their boyfriends.
Meditate on St. Paul’s words about how a husband should lay down his life for his wife as Jesus Christ did for his Mystical Bride, the Church (Eph. 5:25). That’s our standard as Christian men. And with God’s grace, it’s not simply possible but preferable, and much more preferable than any ill-founded alternative the world would propose today.
For more information, see our resources at Chastity.com. I’d also welcome Fr. Thomas Morrow’s book Christian Courtship in an Oversexed World: A Guide for Catholics.