My ex girlfriend never really had a change in personality, I respected the fact that she was having her period and never really brought it up..
Didn't mean I didn't want to have sex with her or anything, as much as I tried and wanted to, she just kept saying, I wouldn't force myself upon her, we'd just lay in bed and kiss kiss kiss kiss kiss kiss, she actually got a rash above her top lip lol..
I'd see her, and just go straight for her, grab her arse kiss her pin her against the wall and just kiss kiss kiss, damn I loved kissing her
But it does suck, because sometimes you are left with extra washing, but it's a part of life and it is required.
Be gentle in those times, they usually feel bad about it - let them know its okay