How to come out as lesbian if I've only been with men?

First of all, LOTS of gay people have had relationships with people of the same sex before. That's nothing to be ashamed of. Most people probably won't think much of it if you tell them you're gay because they'll see that you're sure about yourself. Also the fact that you have dated men and still know you're gay means people can't pull the "well how do you know if you've never tried to date men" thing. Some people may find it hard to accept at first, but once they see that you know who you are and you're happier with women, they'll come around. You're mom or other people who aren't as accepting may try to tell you "but you've been with lots of guys before, so that means you like guys" but as long as you hold your ground and tell them you're sure of it, they'll eventually just have to get used to it. Since people think you're bi already, that makes it a lot easier and in fact a lot of people come out as bi for a while before they're sure about their orientation and then gay if they decide that they are actually gay.
Best of luck!!(*hug*)

 

I'm in the same boat as you: Had straight relationships, didn't really feel any emotional connection or physical attraction, and now hanging out with another girl has pretty much confirmed what I already know, which is that I like girls.

Why not hold off on labeling or identifying publicly with a label? There's no rush. You also don't need other people to validate your sexuality, you know better than anyone what you like and don't like!

 

If you're willing to be open with your mom about how you really feel and why you are sure of your identity I think (or hope) that she would take you seriously. I'm not saying you owe her an explanation, just that talking it over would probably help.