Too sensitive? Or a right to be upset?

OK ladies this may seem like I'm being too sensitive but I would just like to vent a little... I got divorced January of 14 and started dating again in August. I've been with the same guy since August and he dropped the L bomb around Thanksgiving... Anyway I just recently found out he's been talking to other females over Facebook saying things like "Hey cutie what's up" and "You're pretty we should get to know each other." When I confronted him he got really mad about it and basically said it wasn't him saying it blah blah blah. Whatever. I thought we were a serious thing seeing as how he says he loves me and wants me to hang out with him all the time and come to his work and stuff... Anyway I found out yesterday that he went mudding Thursday with a bunch of guys and girls and that whole day I felt funny but he said he was at the shop working on a truck... I mean I just feel really disappointed and different since he lied about those two things. Like I just got divorced from a liar last year the last thing I want is another one you know? Why couldn't he have told me he was going mudding? I wouldn't have gave a shit I don't like mudding anyway so it's not like I would've got mad that I didn't get to go. He said he didn't want to hurt my feelings but what hurt worse was that I found out he lied about it. Ugh. Maybe I'm too sensitive AF is due in 6 days but that just really bothers me.