How can i get out of this rut !?

sometimes i feel really good about myself and im fine but sometimes feel like, in the back of my mind im just not good enough looks and everything and my job . i see girls on facebook that are doing extremely well for themselves they are modelling and looking beautiful all the time and i just feel like a loser, i teach dance but i dont earn alot of money really 200 quid a week sometimes not even that. I have a boyfriend and he loves me to bits and says im beautiful but sometimes just find it hard to believe. I dont strive to be the most beatiful girl anyones ever seen or anything but i want to be able to think im actually ok and have confidence , i try tell myself but just doesnt work . i dont know wether iam like this because my previous boyfriend had cheated on me with several other girls behind my back for the whole five years we were going out or not . My current boyfriend has many friends who girls who are really classy ,lovely looking and have a nice personality, and have a good living and are fun, and his ex was a model and really sweet i just feel like im not good enough for him . Im not outgoing and confident like he is and his associates, just feel like im nothing :'( do i need professional help? ive been thinking this about myself for a long time , feel like i dont think straight any more . im scared icasemy boyfriend wont love me anymore because im not the person he fell in love with , you see we dated when we were like 14 and when i was with my ex for five years he had always been there,he tried to tell me my exe was no good . He said hes always thought i was really sweet and happy and bubbly , and hes never met another gir like me but i feel like ive changed since then .