How to explain period stuff to babe?

So I am lightly spotting and starting my period, I have a pantiliner on. My bf liked to come and grab me over clothes. I felt like I was discharging stuff at the time and he came over and grabbed at me and I was like “Babe! Don’t touch me right now” and he got upset and just kicked out toddlers chair out of the way. He always does this and I don’t mind. But it’s just when you are having some doscharge and the feeling it’s not the best time for someone to touch your croch. I feel super bad and want to apologize and explain to him it’s not that I didnt want him touching me. But how do I explain to him the feeling of period.

Help me out please!