Losing trust in him?...

I was recently out of town for a week, and my boyfriend had been texting me a few times a day about how bored he was since I was gone. I came back yesterday. I immediately saw my boyfriend, and as we hung out, he was texting 3 different girls the entire time. He had been talking to them the entire time I was out of town. He was CONSTANTLY checking his phone for their responses, and he would text them all back instantly. He could tell I was really bothered but he didn't know why, and I didn't tell him. Today it is still really bothering me, I'd just like to know what you ladies would do in this scenario?

--update-- the girls he was talking to were either his exes, or girls he has liked in the past who are now his "friends." Wtf?!