Am I crazy?

Ok so I'm 4 months pregnant and getting married in 9 days! My SO and I had our bachelor/bachelorette parties this last weekend! Mine was out of state and his was just a few hours away from home! We both enjoyed our weekends but we were definitely ready to be back home! We talked a little Sunday night about how our weekends were and what all we did and it sounded great from both sides! Last night we went to dinner and I just had a feeling he wasn't telling me everything bc some hints his brother was throwing so I started fishing for something and low and behold a little tid bit that he failed to mention came out! While he was on his bachelor party he invited a GIRL he went to college with like 6 years ago to come hang out and as far as I know he hasn't talked to her since college! So this girl decides to go to their hotel and bring a friend! My SO swears that he didn't think anything of it and that all the guys there knew her bc they all went to college together! He says I had nothing to worry about bc the girl weighs close to 300 lbs and isn't very pretty (which doesn't make me feel any better)! Ig my question is should I be as mad as I am for him not telling me that this girl (I've never met her) hung out with them one night during his bachelor party and he didn't tell me? Idk if this is normal to be this upset or if I'm just over reacting and being hormonal from being pregnant?? 
BTW:I know he didn't cheat on me bc his dad was there and would never allow that!