Funny enough, I actually did a deep dive on Roman sexuality not too long ago. I put the "It's not gay if there's no penetration" bit because references to intercrural sex (favored amongst the Greeks) and frottage are nonexistent, while handjobs are considered 'spicy' but not really sex - and thus not really 'gay,' since the perception of Romans of 'effeminate' sexuality was centered around sex, not romance.

For that reason, it seems intuitive to suspect that Romans probably didn't regard these acts as sex - if they did, either condemnation (especially of political enemies) or depiction would seem likely, especially with their taste for pornographic artwork.