I'm sorry to hear that you've been having issues with premature ejaculation recently. Usually, premature ejaculation is not caused by any underlying medical problem. Rather, it tends to be related to psychological or social factors. Nonetheless, speaking with your primary care doctor
is a good starting point.
In your case, your story suggests some obvious psychosocial factors for recent sexual dysfunction, namely the stress of finding out about your partner's infidelity. This could certainly be underlying your recent problems with performance. Other factors that can influence sexual performance include fatigue (such as from stress at work or from not sleeping well), as well as many substances, especially alcohol intake.
In addition to considering all of these factors, it would be worth making an appointment to talk with a counselor about what you are going through. They will be able to help you come up with approaches to reduce stress and work through your feelings. Your primary care doctor is also a good resource, especially if you do not have a counselor or therapist
in mind. Most primary care doctors
have good contacts with several, and they should be able to give you some good recommendations.
Good luck, and I hope you can solve this problem soon.