Caught By Girlfriends Aunt

When my girlfriend is away I like to dress up in her sexiest clothes and masturbate.
Last week her aunt walked in the house and caught me in full knickers around my ankles masturbating stood against a wall fantasising that I was a woman having a knee trembler with a stranger she had picked up.
Her aunt said sorry and left, I haven't seen her since but this weekend we will be visiting her. I am fearful as to what will happen. My gf doesn't know about what I do when she is away.