Srimad Bhagavatam Canto 10, Chapter 65, Text 17

SB 10.65.17

dvau masau tatra cavatsin
 madhum madhavam eva ca
ramah ksapasu bhagavan
 gopinam ratim avahan
Lord Balarama, the Personality of Godhead, resided there for the two months of Madhu and Madhava, and during the nights He gave His cowherd girlfriends conjugal pleasure.
Srila Sridhara Svami states that the gopis who enjoyed conjugal affairs with Sri Balarama during His visit to Gokula had not taken part in Sri Krsna’s rasa dance, being too young at the time. Srila Jiva Gosvami confirms this statement by quoting a phrase from the Bhagavatam (10.15.8) — gopyo ’ntarena bhujayoh — which indicates that there are particular gopis who act as Lord Balarama’s girlfriends. Furthermore, Jiva Gosvami states that during the Holi festivities celebrated when Krsna killed Sankhacuda, the gopis Lord Balarama enjoyed with were different from the ones Lord Krsna enjoyed with. Srila Visvanatha Cakravarti agrees with this explanation.
Srimad Bhagavatam Canto 10, Chapter 65, Text 16
Srimad Bhagavatam Canto 10, Chapter 65, Text 18