What does みつどもえの泡 mean?

Question

In the lyrics of 三十路岬,

みつどもえの泡と知りもせず

愛した罪は消えないの

誰を選ぶか決められないと 別れ上手なひとでした

There is this occurrence of みつどもえの泡, which I couldn't find a dictionary translation of. The first line seems to translate to

Without even knowing みつどもえの泡

_{(which is kind of ironic, since I don't know what みつどもえの泡 means...)}

I do know what みつどもえ (三つ巴) means. It's this pattern:

But what does bubbles (泡) have to do with it?

Answer 1

三つ巴 originally refers to that emblem you found, but in modern Japanese it mainly means "triad", "three-way" or "threesome" (e.g., 三つ巴の戦い = three-way battle). In this context 三つ巴 refers to the "love triangle", which is suggested by lines like 誰を選ぶか決められない. In this song, she is regretting that she was involved in cheating without even knowing it.

泡 ("bubble/foam") has long been a common metaphor for ephemeral/transient things in Japanese. うたかた is a more poetic equivalent. Many people have compared bubbles to love, dream, economy or even our world itself. In this context it is used primarily as a metaphor for ephemeral love, but of course it's also a reference to the sea bubbles she is actually seeing.

Therefore 三つ巴の泡と知りもせず愛した roughly means "I loved you without knowing this was a love triangle".

Answer 2

三つ巴 is one of traditional family crest. Soga from Sagami and Utsunomiya from Tochigi were probably the original authors. There are many variations, original one is heading clockwise, another the version of the counterclockwise is called 左三つ巴. This has been famous which had been used by 新選組　土方歳三.

三つ巴 also has some imprecations, one is the three clans are struggling for the supremacy and contain (a hostile power or ideology). In the middle of these powers, one would very difficult to get another. The place looks like this is a vortex has bubbles at the center.

When you play じゃんけん the system looks like this, but it has another name.
See also 三すくみ