During my sexual relations, I ejaculate quickly. It's something that stresses me out in every relationship and causes me to lose my erection.

It sounds like you are experiencing premature ejaculation, which is causing you stress and may be leading to losing your erection during sexual activity. Seeking help from a sex therapist or psychologist can provide you with various techniques and exercises to improve the situation. Some possible solutions may include breathing exercises, squeezing techniques, or trying different sexual positions. Medications are an option but may come with side effects. Behavioral therapy is often recommended as a first step in addressing premature ejaculation. A sex therapist can guide you through these techniques and provide more information on methods such as the squeeze technique and stop-start technique.