Stroking to my gf with a little dirty secret

Last month I realized my friends were stroking to my gf, turns out they have been addicted. Instead of getting pissed that got me real hard. So these days I started stroking together with them to her pics, and it’s so nasty yet so dirty, they go crazy for her and help me out. One of the friends is the brother to my gf and he and I stroke together to her almost everyday now as my gf is in abroad rn, just got back from stroking with him to her and wow do I feel so dirty, but seeing others go crazy for my gf is the hottest thing for me and makes me crazy