I am unable to recall or find a "single word" which describes an unexpressed, mutual love while making explicit the 'frustration' ensuing from that lack of expression, however, the word 'LATENT' or the phrase 'LATENT LOVE' comes awfully close, does it not?
Merriam Webster Online: LATENT: 1) la•tent adjective \ˈlā-tənt\—used to describe something (such as a disease) that exists but is not active or cannot be seen.
LATENT: present and capable of emerging or developing but not now visible, obvious, active, or symptomatic — la•tent•ly adverb.
Origin of LATENT [First Known Use: 15th century]
Middle English, from Latin latent-, latens, from present participle of latēre to lie hidden; akin to Greek lanthanein to escape notice.
Synonyms of LATENT
latent, dormant, quiescent, potential mean not now showing signs of activity or existence. Latent applies to a power or quality that has not yet come forth but may emerge and develop . Dormant suggests the inactivity of something (as a feeling or power) as though sleeping <their passion had lain dormant>. Quiescent suggests a usually temporary cessation of activity . Potential applies to what does not yet have existence or effect but is likely soon to have .
Online Etymology Dictionary:
mid-15c., "concealed, secret," from Latin latentem (nominative latens) "lying hid, secret, unknown," present participle of latere "to lie hidden," from PIE *laidh-, from root *la- "to be hidden" (cognates: Greek lethe "forgetfulness, oblivion," Old Church Slavonic lajati "to lie in wait for"). Meaning "dormant" is from 1680s.
1630s, "condition of being concealed," from latent + -cy. Meaning "delay between stimulus and response" is from 1882; computer sense (latency time) is from 1954.
While you might object to this word's medical connotations, in general, and it's psychological connotations, in particular, I would argue that nothing so resembles a physical disease as the symptoms attendant upon an unrealized romantic love, which are frequently somatic. And from a purely psychological perspective, romantic love shares many of the symptoms of acute obsession, when realized or fulfilled, and sheer psychosis when unfulfilled.
'Unrequited love', is exclusive as opposed to mutual;'Platonic love' is traditionally, one-way and lacks an erotic element; 'Unconditional love', is love that doesn't ask for or expect ... anything; 'unacknowledged love', fails to make explicit the arising frustration you describe; 'mutual, unspoken love' is pretty good, but again, doesn't make the frustration explicit. I am unfamiliar with mutual 'crushes', although such is certainly conceivable; 'skinny love' seems quite close to what you're looking for but is slang (nothing wrong with slang when the situation is appropriate), which I can only assume is not satisfactory since that answer hasn't been accepted.
I hope LATENT, or 'latent love', is more acceptable then the other offerings (no disrespect is intended to the various authors of those answers as your question asks much) because I want, I need, those bounty points so badly.
I'm just now coming to the realization that I may be a latent, certainly a frustrated, bounty hunter!