There is an issue here. The issue is...that being worried about contact is no longer an issue. You have absolutely nothing to lose by asking him....he will hopefully say yes, giving you the opportunity to see your sister or he'll say no in which case you might have to find another dog walking service or perhaps cancel your trip (I hope not...you should go). But either way, why are you worried about contact? If he has someone else already then it's not as though you are ruining the "miss you" value of going dark. Asking won't ruin your chances of anything.
In the end, it's not the years in your life that count. It's the life in your years. Abraham Lincoln
It is hard to fail, but it is worse never to have tried to succeed. Theodore Roosevelt
