I will say right now, I have to experience or anything to support that I know what I'm talking about.
I would think that you being a lesbian will get out in some manner, eventually. Or, even if you just pretend, he'll probably get the sense that you aren't completely sincere. Given this, the truth is probably the best option.
As to him being suicidal, I can't claim to know exactly what's going on, but perhaps if breaking up can ease into a supportive friendship, he would be okay. Maybe even see if you can be with him for a couple nights, just watch movies or whatever... make sure his heart has had a chance to heal a little before he's alone long enough to do any real damage.
But unless you are a good enough actress that you can convince him that you are fully attracted to him, he's probably going to suspect something is off. I'd think it better he know the truth than think you just aren't satisfied with him as a person.