From “just sexy thoughts” to “actual reality” and freaking out

I met my partner 4 and a half years ago. From the very beginning, she openly disclosed she worked as a pro-Domme, and I have always respected her for her honesty and for doing something that must not be either easy or relaxing. It is something people that do not know anything about (friends) fantasise a lot about because their experience is primarily derived from terrible porn videos. She is a traditional Domme, which means there is no sex or nudity involved on her side, although there is sex and nudity for the slave/submissive depending on the activity. I have always respected what she does. Sometimes the sessions are so long and so exhausting that I know she needs time and space to recover. During sex, I am generally vanilla, as she has always preferred a “normal” (can I say anything is “normal” these days?) traditional relationship. We have sex and like many couples after a few years sex does not happen that often. We have also experimented a bit at the beginning of our relationship, mainly me as a dominant male (she is more submissive in private), but with covid things have stalled and we rarely have done anything kinky up until recently.
Out of the blue, one day, she gifted me for my birthday an electric prostate massager. I have always been curious about anal play (even if I am neither dominant really or submissive) and then after some months, she came home in a “mood for sex” and with her work strap on harness and basically pegged me. I have no problem in saying it was a great experience and that it spiced up the sex life. She then started pegging me regularly (almost weekly), and then we have fantasised at times, roleplaying together about me in chastity, me watching her with others, me with my “small cock”, etc… until…. Until one day, she calls me for work and says that she has left her computer at home and absolutely needs something to be emailed to her so I make the mistake of browsing the computer, and the emails, and the messages. A stupid “curiosity killed the cat” moment and realise that she has been chatting to some younger DOM guy somewhere else in the country and they have exchanged photos and “how big he is” and “how much she wants to try with him” “how bored she is” “how much she wants to experience her submissiveness once again” (and these are not the crude sexual messages I have found, but they give an idea) and that she has suggested for him to come to the party she has organised with her other Dommes friends to celebrate some local event. But the worst part is that she openly discusses with him (and as a matter of fact with at least 2 other colleagues!) how much she is turning me into the perfect little cuckold, adding that for me “next is a nice chastity cage”. Yes, she also tells them how much she loves me and cares for me and that she does not want to live with anyone else, but, at the same time, she is definitely wanting me to accept my new role within the relationship.
Many things happened: 1) I had a massive erection 2) I started crying 3) I felt like I was going to die 4) I still had a massive erection.
With all the emotional turmoil and the fact that I had no intention of letting her know what I had found out. We have moved forward on roleplaying and she has at times made me try – to play – a chastity cage and also that the “special event” is looming…. In fact, it’s in two weeks (and it happens to be during my birthday weekend). So, with my massive erection, I am incredibly conflicted, nervous, panicked, scared. Do I just let it happen?