HELP ??!!

The guy I am dealing with now , he is 25 I am 20. We started off having sex barely even knowing each other . I assumed it would just be a one night stand , but boy was a wrong . Either the sex was really good , (mind blowing for me actually) or he just really wanted to see me a lot more because that one night stand turned into seeing each other every day , sleeping over at each other's houses , going out on cute dates , exchanging birthday gifts and exchanging gifts on Valentine's Day. We have talked about a relationship and he always says he wants to take it slow because Everytime he rushes a relationship it doesn't work out and he just wants to get to know me better . Well , we don't go through each other's phones or anything and we have always said that if we we're talking to anyone else we would let one another know for health reasons as well. (Sex you know) . Well I feel like we basically date , I mean regardless of what the tire is I feel like we are together , because at the end of the day we are always together , asking how each other's day was , missing each other the whole 9 yards . Well while he was at his semi pro football game today he left his phone in the truck and I decided to go through it . I saw he has been texting other girls and i even read one messages where he asked one of them to hang out . Im so hurt but then again I can't be because we are not together . I know I had no right to go through his phone but im very curious by nature .