Africa is a big continent with a long history, you may have to be more specific if you want a definitive answer...

What time periods and what regions? This is such a broad question...

There are a variety of ways to answer this question. I'm going to take it face value first, and point you to some sources. As others have noted, Mark Epprecht's work is very good. His volume Hungochani has a very interesting opening chapter on pre-colonial male-male relationships in the area of modern Zimbabwe. Another place to look is Stephen Murray and Will Roscoe's edited volume Boy-Wives and Female Husbands: Studies in African Homosexualities. Arguably, it's a bit dated, but they have really interesting introductions to male-male and female-female relationships in different regions before the more specific chapters. Most of the chapters are admittedly focused on modern era, but the introduction to "West Africa" for example digs a bit in the deeper past.

But now let me essay a second way of answering your question. Part of the difficulty is that "homosexuality" is really a term that evolved to describe particular types of same-sex relationships in the Euro-American context. Clearly, for other historical contexts it's as bad a fit as, say "empire" or "university" might be. In other words, there is deep evidence of a lot of same-sex intimate types of relationships that might or might not have involved sexuality within that intimacy... blood brotherhoods, female husbands, boy-wives, royal pages with ritual obligations, etc. Similarly, there's evidence that situational, one-off same-sex sexual relations were not stigmatized to the same degree in different places and times. Are these 'homosexual'? (does male-male prison intercourse mean that both parties are actually 'homosexual' in our country today?) It's difficult to answer because the term denotes something pretty specific for us, and doesn't really apply well. But scholars are parsing this out pretty carefully where they can, and if you start with Murray/Roscoe and Epprecht you can follow a pathway of their work so far.