I second Mary Ellen’s suggestion. It’s best to put your cards on the table, so to speak, when dealing with relationships with people that might become sexualized.
I notice that you didn’t mention your state in life, e.g., are you single, or are you married? The answer to that question would put the sort of sin that you are being tempted with at different levels. If you’re married, you have absolutely no business being with this lady in any sort of situation she (or you, for that matter) could easily take to another level. If you’re single, you first need to determine whether you are called to marriage. That includes determining whether you would be a good husband and father. All this is called discerning a vocation. Don’t let that term scare you: There are three vocations in life: The consecrated (including ordained,) the married, and the single.
If you discern a call to the married state in life, you’ve got half the battle “won.” The next thing you need to learn how to date in a chaste and appropriate manner.
From what I see nowadays, the institution of dating and courtship seem to be dead in the water. The purpose of dating and courtship is to get to know a member of the opposite sex for the express purpose of determining if they are a candidate for marriage to you, or to anyone, for that matter. That would include getting to know their core values (just determining what religion they practice isn’t enough,) discerning whether they would be a good life partner (which would include such things as being a good team worker,) and figuring out whether they would be a good parent.
Assuming you’re single, and in a position to get married (education complete, reasonably stable source of income, emotionally independent of your parents,) there is no way to do the kind of discernment that I described other than dating. So you’re going to have to learn to deal with sexual feelings without giving outward expression of them. That’s part of learning to deal with temptation. Just because you’re attracted to someone does NOT mean that you HAVE to hop into bed with them. Emotion is a powerful part of our personalities, but remember, we were given free will, a gift we share only with God. We’re expected to exercise our free will in making good choices instead of sinful ones. Current society places far too much emphasis on expression of emotion. If we all lived our lives with feelings that were uninhibited by our intellects and our wills, the streets would be littered with bleeding bodies!
What I’m about to say might sound a little condescending, but I honestly believe that young people have no idea how to date. A date isn’t just “hanging out.” Lack of a preplanned activity and boredom is generally how people start experimenting sexually. Our reproductive systems are meant for sexual expression that is both unitive and open to procreation in the context of a stable marriage. They aren’t a built in free home entertainment system, although that is how a lot of people treat their sexuality. The human reproductive system is the body’s lone exception to the rule “use it or lose it.” Nobody ever dropped dead of chastity, but there is a worldwide epidemic of such things as incurable venereal diseases!
Find out what this (or other) young ladies’ interests are, and invite her (or other “hers”) to do something that might be of mutual interest. I’m thinking in terms of museums, festivals (the summer festival season is coming up, where you can go to exciting activities,) concerts, theaters (many places have outdoor concerts or plays that are not expensive or are free to attend,) and participate in the planned activity with her. Even an evening of something like bowling or a sporting event is good, and will give you plenty of information about the other individual (e.g., is she a good sport?) While you’re at this activity, observe how she acts.
When I was dating, I would discreetly notice such things as how my date treated waitresses and waiters, what his manners were like, whether the topic of conversation always revolved around himself, if he could take minor frustrations in stride, if he could converse intelligently on a number of things, whether he could converse (as opposed to monopolizing a conversation,) whether he was considerate or inconsiderate, and the like. Answers to those questions, I figured, would give me an inkling of how, if the relationship progressed to marriage, he would eventually treat me. I weeded out a lot of potentially unsuitable candidates that way. Making it clear that I was not into premarital sex was another great way to weed out unsuitable candidates. Sure, it resulted in a lot of men not calling me for a second date, but I figured I didn’t want to be involved with anyone that selfish anyways. A self-centered person makes a lousy spouse. Someone who doesn’t respect the other persons’ values makes a lousy spouse. Finding out all this information early on is a good way to save yourself time and heartbreak, as well as sin. And by the way, I got this hint from a religious Sister who worked at the parish I attended when I verbalized my frustration in finding suitable men. God bless that Sister, who taught me that there is a lot more in discerning a potential marriage partner than just finding a knight in shining armor! In your case, beware of damsels in distress: Generally, you end up with a distressed damsel!