Basically, "同性恋" is the direct meaning of homosexual. However, it is quite difficult for Chinese people to say this directly.
There is an old saying in Chinese, called "不孝有三，无后为大". Here, it says that having no children is the worst thing for a person. If you have no children, then it's impossible for you to show filial obedience to your parents.
Since it is almost impossible for homosexual people to have their own children (I mean children with DNA relationships). Thus, a lot of Chinese people, especially old people, regard homosexual as a thing that cannot be said. So if you say that someone is "同性恋", then some people will regard this as slur. But to some other people (like me), this is not slur.
If you say someone is "玻璃"(the original meaning is just glass), then it means that this person is homosexual. I have to say that this is a slur.
Some people use "基佬" to refer to gays these years. But this word is common only in young people.
However, if you are talking to Chinese people, you have to consider whether they can accept homosexuals or not. If you think that they cannot accept homosexuals, it's better avoid these topics with them. It might cause unhappiness between you guys. But if you think they can accept homosexual, then it's okay to use "同性恋" directly, and I don't think that they will consider it as a slur.