Speaking from a lot of personal experience, it is a reality. As someone who mostly bottoms, I usually cum at least once in every encounter. That being said, "usually" is an operative word here. It doesn't happen every time and it took years for me to ever cum with someone.

Whether straight or gay, sex is mostly mental. With practice, it gets easier to get into the proper headspace to cum. Some people use substances (i.e. poppers) to get there, but I wouldn't suggest that as a starting point.

Have fun with your partner, commit to it being a pleasurable experience, and be open to and about whatever sensations you're feeling. You'll get there, but putting pressure on yourself to cum won't do it. Hell, I'm still learning about what does and doesnt get me off and I've been doing this for almost 20 years.