He's in with a guinea pig, thats a big no no, he's probably starting to feel his hormones, rabbits dont like being picked up and he probably got cross with you. He will start to become more fiesty when he hormones kick in and your guinea pig is in danger im afraid. Id have him neutered when he's 4 months old or when he weighs enough and he'd be happier with a female neutered bun.
Lots of rescues get far too many guinea pigs coming in that have been kept with rabbits with fractured pelvis' due to the bunny mounting them and other awful injuries, they are different species and dont understand eachothers communication. Theres a thread on here about the other dangers and nutritional problems about keeping these animals together if you want to have a look.

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An old man walking on the beach at dawn noticed a boy picking up a starfish and throwing it into the sea. When asked why, the boy explained that the stranded starfish would die if left to lie in the morning sun. ‘But there are millions of starfish on this beach' said the old man. ‘How can your efforts make a difference?’The boy picked up another starfish and placed it in the waves. ‘It makes a difference to this one.' he said