Many learned authors have written scads of words about ancient Roman romance, and it's safe to say that they seldom agree on anything. This is understandable -- the authors are trying to cover a period of more than a thousand years (even if you include only the time between Rome's mythical founding by Romulus and the departure of Constantine for his new capital), and a huge geographic area, and a wide variance in classes and cultures. It's essentially equivalent to defining "romance" in the English speaking world -- starting in London before the Norman Conquest and ending in Hollywood and San Francisco today. "Experts" have to be very selective to avoid being buried in the "romantic" data. Honest authors chose strictly limited geographic and temporal parameters and announce them openly, but what they choose tells us more about the authors than about the Romans. The various authorial biases are available on the Internet as well as in hard copy books.
What is safe to say is that, in different periods, places, cultures and classes in this wide-ranging "ancient Rome", just about every possible variation of interpersonal interaction had its adherents.
Many variations existed simultaneously. There were no overriding norms, although there were long-lived "ideals". Mature men should demonstrate a manly interest in any fecund females in reach -- a culture that existed on conquest and enslavement, that relished mass mayhem as entertainment in the amphitheaters, and whose origin mythology validated mass rape could be expected to produce overly aggressive males. On the other hand, women of all ages should be like Cornelia, the daughter of Scipio Africanus and the mother of the reforming Gracchus brothers, who was a republican archetype for the three great Roman feminine virtues: pietas (dutifulness, dutiful conduct, piety, patriotism, devotion, kindness); pudicitia (modesty, chastity, virtue); and concordia (agreement, union, harmony). In most places, times, and classes of Ancient Rome, by the way, only the first of these three virtues was considered even to be appropriate to, much less desirable in, mature men.
In the upper classes, that is among the old senatorial, cavalier, and rich merchant families, many marriages were arranged to increase family power and wealth. That didn't completely eliminate romance between spouses, but pietas -- duty to family in this case -- sometimes took precedence. Spouses in such marriages might seek romance elewhere, the women, most often, prudently and the men, more often, raucously. And sensual pleasure might be sought at yet other doors. There were no necessary links among marriage, sex, and romance.
Attempts to regulate social interactions were made -- huge numbers or Roman laws touched on the subject. And that they were largely ignored is shown by the fact that the laws had to be reiterated repeatedly.
Kissing: Public displays of affection were definitely déclassé -- only on strictly defined occasions was a real kiss deemed appropriate in public. Just as it is today, the side-to-side "air kiss" (called the osculum, meaning "little mouth" or "pucker") was common as a form of greeting, but it was not considered significant. You might also kiss a hand, ring, or foot as a public sign of submission. It was your duty to bestow a final kiss when a friend or relative died to release the spirit of the deceased. Little kids were always huggable and kissable. But "real", that is, passionate, kisses should be private and always were significant.
Real kisses fell into two categories. The basium was the direct lip-to-lip kiss between lovers (and this Latin word is the source of the cognate words in most European languages -- bacio, It.; buss, Eng.; beso, Sp.; baiser, Fr.: etc.) The basium was the discussible kiss and the kiss memorialized in the polite poetry of the time. The other kiss, the saviolum, although often literally translated as "little kiss", was really the more passionate labio-lingual kiss that the French inherited from the Romans and that we, therefore, call the French kiss. It was always a prelude and an invitation to further interaction. Circumlocutory words like suaviolum ("little sweetness") or salveolum ("little greeting") might be used, but everyone knew what they were talking about. Catullus memorialized the saviolum -- and a lot more -- in his coarser poems. The only time a public saviolum might be barely acceptable was at the end of the multi-day betrothal ceremony/party, and even then a basium would have been used in "polite society". That betrothal kiss sealed the marriage in the eyes of the witnesses and effectively ended the putative virginity of the bride.
At times, of course, a passionate public kiss might also be purposeful affront to society. And, déclassé or not, passionate kissing in public became common enough to be mentioned by authors of various periods in the history of Rome as a scandalous habit. A particular place in the forum in Rome -- in the Vicus Tuscus, just east of the Basilica Julia -- was identified as a location where it was frequent. That was where the fast crowd hung out and where men went to find professional assistance. Ironically, the house of the virtuous Cornelia had stood nearby, before Julius Caesar demolished it to build his Basilica.
Roman Marital Customs: http://ancienthistory.about.com/homework/ancienthistory/cs/marriage/index.htm
Legal status -- women, family, and children: http://www.uky.edu/ArtsSciences/Classics/wlgr/wlgr-romanlegal.html
Diotima -- Roman women: http://www.stoa.org/diotima/essays/#rome
Catullus -- the poems, in English: http://www.vroma.org/~hwalker/VRomaCatullus/list.html
A modern kiss glossary -- learn all 20 kinds!!! http://www.pocketstuffer.com/kgloss/
And, finally, the scandalous behavior of our Bonobo cousins: http://www.libfind.unl.edu/rhames/bonobo/bonobo.htm