Translation:My boyfriend loves cats.
For your information, "男朋友/女朋友" only means "boyfriend/girlfriend" in romantic relationship. These two words can also be "男友/女友".
If you just want to describe the gender of your friend, use "男生朋友/女生朋友" Although I myself would start to be curious if you intentionally emphasize the gender xD
so here, 生 serves exactly what purpose? like... boy organism friend?
Another tip about using 爱. According to my mandarin teacher(from nanjing), most chinese dont use 爱 that often. usually they'll use 喜欢(Like) b/c they feel 爱 is very strong and can only be used to describe emotions towards family members or spouses(or gf/bf).
Not sure why that was down voted, as it's exactly right and that's a great point you make. Actually, I think tge word love in English is "softer" than most of the other languages I've learned
In context it could be just one cat that is understood by the speakers: "I have two birds, a dog and a cat; 我的男朋友爱猫 (my boyfriend loves the cat)". But unless it's clear what cat they're talking about you'd be more likely to hear "我的男朋友爱那个/这个猫".
I realize 'boyfriend' is the expected word in this sentence, but hypothetically, what if somebody has more than one boyfriend (hey, these things happen)?
Is "My boyfriends love cats." wrong? And if so, how would one say that instead?
A good sentence to communicate that you have multiple boyfriends and they all love cats would be 我的男朋友都愛貓。
‘们’ can be used as a plural for all people. 孩子们, 学生们, 男朋友们。i have also seen it used with rabbits and birds as a plural, so presumably it works with cats as well (presuming the need to specify the plural)