Guys always cheat with me?

and its more emotional then anything else but it always happens and idk what it is or why it happens but I always let them! I always make up excuses for them too like right now I looove this guy and he's liked me for about two years and we talk but he's had a girlfriend for like almost a year and he's been talking to me for like nine months but we don't have sex or anything and he's stillll with me but won't leave her. and this isn't the first time I've had this happpen. soooo confussed guys!