Periods and Date Nights... Advice?!?! 😳😬

Elizabeth
(( I don't have a good relationship with my mom, so I was hoping that some of youse would give me some advice?))
Hi Ladies,
      Should I tell my bf when I'm on my period?  We are both virgins(and I'm not having sex until I am married), but he does grab my butt when we watch a movie.  He has also put his hand in the very back of my pants.  However, it "stays pretty high up". 😳  I was not on my period at the time, but I need advice if we cuddle and I do have "it".👀😳  
Do you tell your bf, if you're on it?  
We have really good communication; so is it normal to-ya' know...... "give him a heads up".  For example, should I tell him "I might get moody, b/c I'm on my period."?  If you think I should... please advise me how I should "warn" him.  Thank you so much!! I am so sorry about all the reading, but your replies are greatly appcreated!!!!!
Extra Details••••
We have been dating for 4 months.  He is my first "real bf"; and I'm his first "real gf".  We have movie dates and have already gone to his prom (he's in 12 grade--- I'm in 10th grade).  Our families have met and gotten along really well.  :)