Without having read the 'love sick the series novel', it's hard to say exactly who the main characters are. However, considering it's about love, there might be a protagonist who is experiencing a strong and perhaps complicated love. There could also be a love interest, maybe a friend who gives advice on love matters, or a rival in love. These types of characters are common in love - centered novels.
I'm sorry I can't name the actual main characters in 'love sick the series novel' since I'm not familiar with it. But typically, in a novel series about love, you would expect to find a central character who is the focus of the love story. This could be a male or female lead. There may also be supporting characters such as family members who influence the main character's view on love, or other friends in their social circle who are also involved in their own love situations and thus interact with the main character's love story in different ways.
I don't know the specific main characters in 'love sick the series novel' as I haven't read it. But usually, in a love - themed novel series, there could be characters like a young couple, or a person searching for true love.