Comments I received when I asked this on the askgaybros subreddit:
"Lived in Pakistan so can't speak for all Muslim countries but:
Topping is seen as gay but less dishonourable than bottoming.
I strongly do believe that yes, sexuality quite often does depend on availability of women. Education in Pakistan was gender segregated until the age of 16 ish. Before that, there used to be boys in my grade used to get it on with each other.
2 men having premarital sex is definitely seen as more sinful than man and woman doing it. But men having premarital sex is not even talked about so I guess there is less risk of bringing that "dishonour".
BBC has a great documentary called "How Gay is Pakistan?", where they show how a lot of men who have gay sex actually don't consider it as part of their sexuality (this is of course bs and internalised homophobia). It's more like a sexual relief thing."
And:
"As a European who has been to Morocco and had sexual fun with local guys over there, without even having to ask them "are you gay?" or "you into guys?", I can confirm the fact that men have sex with each other prior to marriage with a woman as a cultural norm.
Sex with another man is not considered pre-marital sex. This gay sex before marriage is an extremely common, widely-practiced part of their culture - and a very ancient tradition. Probably if you asked most straight-identifying Muslim/Arab men, they would deny it or say they know nothing about it, but believe me (from my own experiences in Morocco) - it is true."