Is he cheating? Or is she just a friend? ?

Well my boyfriend for about a month and a half now has been talking to other girls, but there is one girl I'm worried about. She always is around him, she texts him a lot and tags him in a lot of pictures on Facebook. Him and her both claim that they are just friends, but is that really all they are? The girl is way more closer to his family than I am so that scares me. I even think his mama likes her better than me. He says he only loves/likes me but Is that really true?? He always spends time with me, but yet he spends time with her too. What do you think??