It wasn't out of the ordinary for a Roman man not to have a male lover, there were lots of ancient Roman men that stuck with ladies. Rarely would you get someone who was exclusively gay. Men were expected to marry women--a man wanting to marry another man in ancient Roman society would be incredibly out of the norm.
Homosexuality was usually seen in army legions, where there were no women to make those lonely nights go by faster. It was more of a situational thing than it was an actual 'lifestyle', for lack of a better word.
Also, the 'bottom' guy would typically be stigmatized in a negative way for taking the women's 'role'.
People act like ancient Rome was just one huge gay orgie, when it really wasn't. That's ancient Greece.