4 Stages

Happy Valentines Day! Recently I've been giving a lot of thought to relationships, and this is some of my musings. (I ran the framework for this model by my spiritual director, so it's officially okay-ed by a very holy priest.)

Guidelines to Healthy, Chaste Relationships

Stage 1: Dating
The purpose of this stage is mostly to have a good time. I don't mean to use people, but to really enjoy the presence of the amazing people in your life of the opposite sex. This entails going to coffee, having lunch, or even dinner and dancing if that suits you. You can date as many people as you want at one time as long as things don't get physical. Physical affection should be limited to brief, friendly hugs and perhaps some hand-holding. That's right: NO kissing and absolutely nothing sexual. (Note: beware of dancing! Although it is within the parameters of this stage, it can lead very quickly to intimacy.)
Keep it lighthearted and fun. The focus here is getting to know people and casually considering them for a more serious relationship. Gals, avoid projecting way far into the future. It's totally unnecessary in this stage. That being said, if there is anything that might prevent you from wanting to commit yourself to this person, now would be the best time to discover it, before too much emotion and physical closeness (damn that cuddle hormone!) has clouded your judgment.
If strong feelings do develop, you should either allow your relationship with this special person to evolve into stage 2 or, if the person doesn't like you back :( then it's probably time to break things off. In general, it's healthier to not pine away for someone endlessly but rather to move on with your life and find someone who deserves your love.

Stage 2: Courtship
The purpose of this stage is to consider your significant other for marriage. You are exclusive now (that means no serious one-on-one time with people of the opposite sex), and kissing is allowed (unless you belong to that group that chooses to save their kisses for marriage). Cuddling is also (yay!) allowed here. I suppose in this stage the dates get a little more involved, too.
Be careful, though, because I think that some of the strongest temptations occur here. The discovery and presence of a mutual attraction can be so exhilarating that it may be easy to get carried away. It is even more important to guard your heart here, and your significant other's heart. As Jason Evert so eloquently put it, "The real measure of love is doing what’s best for the beloved." You should seek to help your beloved grow in virtue, not tempt him/her away from it, and if s/he is tempting you away from virtue then you probably need to break things off. (This is not to say that passion is a bad thing. If, for example, you find your significant other outrageously attractive and that tempts you away from virtue, that temptation would not be grounds for breaking up. Actually I am of the opinion that this chemistry is a very good thing. What's dangerous is pressure from him/her to go farther than you know is right.)
Courtship is not marriage!! I know it seems obvious, but it's important to keep in mind that even though you're exclusive, you're not completely committed, either. This means that you needn't spend every spare moment together or stop looking at other opposite-sex friends as possibilities. There's no need to ever stop looking until your wedding day, honestly (and by then you should be totally ready and willing to give up looking, anyway). All's fair in love and war, and if you or your significant other think they've found someone better, you should both be free to move on, heartbroken as the other may be. In truth, it's probably better to let someone go who's not sure about your relationship than to hold on to them. Freedom is of utmost importance in the realm of relationships! For after all, it is only with complete freedom to choose that we can fully choose to love.

Stage 3: Engagement
Obviously I've never experienced this stage (or the next), but I'll try to outline as best I can.
When you are fairly certain that you want to spend the rest of your life with the person you're in a relationship with, then hopefully s/he'll feel the same way and agree to marry you. I definitely think that the responsibility to pop this question falls on the man of the relationship, but this is a whole other issue that I really don't feel qualified to get into.
If courtship is an evaluation, engagement is a scrutiny. With marriage on the horizon, you must do everything you can to establish that you are 100% sure that you want to bind yourself to this person for eternity. Ideally you'll be going through some very thorough marriage prep with a good priest and spend lots of time in prayer to continue discerning whether this is truly the right path for you.
There is nothing additional in the physical affection department during this stage, and in fact it may be better to back off a bit physically in order to more deeply consider the other aspects of your relationship.
If all goes well and you still know that you want to marry this person, then you'll be ready for the 4th and final stage...

Stage 4: Marriage
From the moment that you take your vows, you two become one heart to love and to serve. It may seem incredibly romantic at first, but the love of married life is primarily an everyday, day-to-day love, grounded in the simple, mundane things that occupy your lives. This is why it is inappropriate to live together before marriage; part of married love is sharing every aspect of your lives together.
With your marriage vows, you are also finally allowed to go much, much farther than kissing... The unity of the bodies of man and wife in the marital act is essentially a renewal of the marriage vows and an outward sign of the union of their hearts. This is why it is inappropriate outside of marriage; in any other relationship it sends a false message and makes a hollow promise.

So, there it all is. Hopefully this has made things clear. I think where a lot of people run into trouble is mashing the stages together in that strange conglomerate of doing what feels good. A bit of discipline, however, is very freeing and (from what I've heard) totally worth it. If you've got questions please do leave me a comment, and I'll edit or comment accordingly. And definitely if you have further insights, please share. :)