There's a Baal HaTurim on Exodus 19:4:

ואביא אתכם אלי מה אשה נקנית בכסף ובשטר ובביאה אף ישראל כן. ... בביאה זהו שנא' ואפרוש כנפי עליך וגו' ואבא בברית אתך לכן אמר הושע ג''פ וארשתיך לי: ואביא בגימ' בביאה

I found this quite surprising, as while there are many references to God and Israel being married, I don't recall seeing intimacy referenced before. That's in line with how Chazal generally avoid ascribing such intensely physical things to God, even as an anthropomorphism (e.g. God smells our offerings, but does not taste them).

The Artscroll Baal HaTurim does not say this is based on any prior source. Is there any place in which intimacy with the Jewish People is described in Tanach or Chazal?