Can you write a heterosexual relationship? Yes? Problem solved.
Seriously though, a gay couple isn’t any different than a straight couple. If you’re really getting into detail with a make out scene there’s different moving parts (heh) but the way people love each other is all the same. The only differences a homosexual couple will face are all societal. It may take them longer to get together because one isn’t sure of the other’s sexuality, they may be less public about their relationship because of hate but the fundamentals are all the same. If you are struggling just focus on the feelings. Think of a relationship that you have had that is similar to the one you want this couple to have, and use your own feelings to understand and write for theirs.
In my novel this is my couple’s first relationship with another girl, so I think about how cautious I was in my first relationship, how I was so afraid of doing something wrong, and how giddy I got just from holding hands. I take those feelings, and take into consideration how nerve wracking having a relationship as a lesbian couple in the 1650s would be, and BAM, I have my relationship.
Even though the fundamentals are all the same, I would recommend interviewing friends and watching youtube videos about LGBTQ taking about their struggles so that you have a better understanding from that perspective, don’t assume you get it. It will make your writing a whole lot stronger to draw from other’s emotions and stories.
If you are cisgendered and are writing about a nonbinary or transgender person, that’s a whole different story that I will save for another post. I will say that with this even more research would be required, and do not skimp on those videos and interviews. They have experienced feelings that you have never had to experience, and that is not something to take lightly.