Having scored four tries before the break, Saints found themselves under severe pressure as Gloucester fought back, with George Hendy, Tom Pearson and Tom Lockett all sin-binned.
“At half-time we had the same conversation as last week – we knew they were going to try to come back and that happened,” said Belleau, who will vie with England’s Fin Smith for the number 10 shirt.
“We were in trouble in our 22 and undisciplined, I think it was three yellow cards and we needed to put two backs in the scrum.
“We just tried to keep fighting for each other and stay connected as a team.”
Having won the title in 2024, Northampton are fourth in The Prem table after two games, with an East Midlands derby against Leicester Tigers at Franklin’s Gardens up next on Saturday.
Belleau said: “I know it’s the game of the year at home, a derby. I know how important this kind of game is. It’s the same in France, we love these games.
“It’s going to be a big day for us and let’s try and get a win because we missed the first opportunity at home (against Exeter).”
Belleau has now made three appearances for the club and added: “It was a very exciting challenge for me to come here and I am enjoying it a lot at the moment.”
