‘Love Is Blind’ star Brittany Wisniewski shocked her boyfriend back home in Maryland when she hooked up with Mod sun in Los Angeles… because we learned the man thought they were in a committed relationship.

Sources familiar with the situation tell TMZ … Brittany has a very friend on the East Coast, a hunk named Rocky Hawkinsand they have been in each other’s lives romantically for four years.

We’re told Brittany and Rocky had been separated for six months in the past, but they reconnected before she left Maryland for a two-week filming of “Love Is Blind” … with Rocky taking her to the airport drove to send her away.

Our sources say that once the reality dating show finished filming, Rocky picked Brittany up from the airport and they reconnected romantically… with their reconnection well known to family and friends in Maryland.

We’re told Brittany recently told Rocky she wanted to get more followers on social media to make money from brand deals, so she signed up for ‘LIB’… and wasn’t on the show to actually find love, because she was. in a romantic relationship with Rocky.

We’re told Rocky drove Brittany to the airport last Monday for her flight to Los Angeles… and our sources say she told him she was coming to LA because Snapchat invited her to tour their headquarters as part of her aim to build her followers on social media.

Our sources say Brittany told Rocky she’d be hanging out with another ‘LIB’ alum … and he was shocked to find out she hooked up with Mod Sun after attending his performance at The Wiltern on Monday night.

TMZ broke the story…video shows Mod Sun and Brittany kissing and canoodling at a bar in West Hollywood.

We’re told Rocky was sitting in his office this week when his phone blew up… people sent him a news article and photos of Brittany and Mod Sun together.

As we reported…Brittany and Mod Sun too went out to eat Tuesday evening, hand in hand on the way to a steakhouse.

Our sources say Rocky contacted Brittany when he saw her with Mod Sun… but she hasn’t responded yet.

Rocky, we’re told, is in absolute shock… and our sources say the feeling is shared among their group of friends.

We reached out to Rocky, who tells TMZ… “We were in a relationship before and right after the show aired. We were knowingly in a committed relationship. I’m completely blindsided by all of this leading up to it moment I dropped her.” went to the airport last Monday for her trip to LA. There is no other option.’