I have yet to have seen any evidence that these two were lovers.
Likely some few of the thousands of e-mails between the two included messages of a more personal thrust, so to speak.
“Last night your big teeth were particularly busy, my love.”
“And your stroke, Mr. Strzok-—who wouldn’t, um, crack under such a technique?”
Reckon it will all come out in due time.
They sent each other over 300 texts a day. Only 15% (IIRC) were passed to the committee and even those had personal (pillow talk) redacted.