I smoke a lot. My brother says that in the future I may have problems in sex because of this. How can this be related? I'm fine with it now.

Your brother is right. Smoking is killing you slowly. Besides, smoking contributes to peripheral vascular disease, which affects blood flow to the genitals. It's better for you to quit smoking. For better intimate life it is necessary to lead a healthy lifestyle. Don't use alcohol, eat right food, gp to sport. To increase your sexual life you can try such tips https://blog.uberhorny.com/what-men-can-do-to-make-their-orgasms-even-better/ and choose the best for you.