Since I first read the original message, I was hesitant to respond at all. I'm not male, but I'd like to add my 2 cents, even so.
I turned your original question around that considered how I would feel if I learned that my spouse had been "making out" with another man in my absence. The answer for ME is a resounding, "Hell, YES!" Infidelity is infidelity, whether it's with same-sex or hetero contact. My honest feelings about it have nothing to do with sexual orientation, whatsoever, but more with commitment, trust, honesty, integrity, and propogation of a healthy relationship and my feelings apply to my Self, only. If the topic is resolved between consenting adults, there should be no jealousy or negativity associated with it as long as the topic has been discussed, understood, and agreed-upon.
Some people are "comfortable" inviting/sharing additional sexual partners, and I have no judgement on that, except to say that it can be very, very risky emotionally and health-wise. Because human beings are inherently flawed, we can fail to remain unattached to sexual partners and that opens up a whole new can of worms. The health issues are enough to scare the be-jeepers out of me, personally.
I do know that such sexual activities have been known to become extraorordinarily abusive to all parties involved, under certain circumstances. My ex was constantly after me to allow him to bring another man into our bed and, thank God, I refused for 14+ years because I was completely uncomfortable with the idea. For me (and nobody else implied), it would have been the ultimate humiliation, degradation, objectification, and abuse possible at the insistance of my former abuser and there is much more to that story that there is space on this forum. For many, it's an uncomfortable subject and can only be visited in individual fantasy. For those who are comfortable with it, more power to you! Just be safe and respectful with, and to, your additional partners.
Best wishes to all!