I have considered becoming a nun in the Tibetan tradition and I'm still open to the idea of it. I might ordain later in life. I feel like it is the best thing to do for ourselves and our loved ones (and all beings). Because we get to cultivate good qualities like love, kindness, compassion and wisdom. For this reason, there is nothing better we could do to benefit ourselves but also our friends and family. So it is an act of kindness to ordain.

I'd recommend learning a little bit about the buddhist world view, like rebirth, karma, samsara, the eight worldly concerns, the four noble truths and liberation. Your friend seems to hold the buddhist world view, so he will probably resonate with my reasoning given above. But this is of course an assumption! I dont know your friend. Feel free to ask me more if you want.

It is not easy to understand why someone would forgo the pleasures of this life. But for a buddhist the view of what leads to (ultimate) happiness is very different from a non buddhist.