Sex help

So i need some advice or help on this.. when me and my boyfriend are like in the moment of having sex.. like I'm in the mood and im into i a lot .. i love it so much...  but then for some reason i can be like really horny and wet and then out of no where im like dry .. and then its like a turn off for me because im not wet as im supposed to for my boyfriend and he enjoys it when i am.. also im only wet like a lot but he trys to make me squirt and im not sure how to or how it works?? Help me!!? Thank you in advance