Oh, honey. First, I am sorry you find the need to be here, but am glad you found us.
My situation, early on, mirrored yours. It escalated in devastating ways. Devastating for me and our kids, but also for stbx.
Your husband is cheating with high-risk sex partners. You have all the proof you need. More will not change anything,
That said, you can acknowledge that, protect yourself from disease (do NOT have unprotected sex with him--oral, vaginal, or otherwise--either; The consequences are devastating.)
You can then take all the time you need to get your ducks in a row. You don't have to make any life altering decisions today, tomorrow, or until you are done with your exams.
But please--for your physical and emotional health, DO make the choice to believe the truth and take measures to protect yourself---physically, most importantly, but also emotionally.
I did not do this, at huge physical and emotional cost. Really, just a shift in my own thinking made a huge difference. Trusting myself, accepting I could only change own thoughts, feelings, and actions made even a rocky home life very different for me. I not achieve this shift for a very, very long time.
It did not change my husband's trajectory. That's his job. And yes, the behavior (very well hidden) escalated. Eventually, our marriage ended--very badly.
You have proof. You have lots of proof. You don't need more-you need a plan.
You can tackle it from the make-the-marriage-work place, which requires a partner willing to do the hard work with you. Or you can get your ducks in a row, in preparation for ending the marriage.
But you cannot have a healthy marriage with emotional intimacy and love -- not with a man engaging in high risk extramarital behavior that is apt to escalate over time.
Don't do what I did. Don't sacrifice your young and middle adulthood to a marriage that is a sham. Make the marriage YOU want, or give yourself the opportunity to move forward constructively. Certainly, if you need time to prepare for this, take that time. But don't permit yourself to "believe" (code for being too scared to rock a boat that desperately NEEDS rocking if it's ever going to right itself and sail smoothly) that better-hidden behaviors are not occurring. I can guarantee--seriously, I would bet everything I have--that your husband will not and cannot stop this type of sexual acting out and will escalate if he does not make the decision to get much needed help.
This cannot be overemphasized: no unprotected sex. As long as you are with him, have routine, scheduled STD testing every six months--more often, if your doctor recommends. (Be sure your doctor knows he's having sex with high risk partners.) Consider some IC to help you figure out what is important to you in this life and how to assert yourself best, in order to achieve it. I would not bother with MC until and unless your husband acknowledged his issues and spent some time in IC--preferably with a CSAT--first.
Millions of hugs to you.