TL;DR I cant tell my gf of 2 years I cheated on her and I know I should tell her
My brothers (25M) gf (26F) and I used to hookup when I was younger (I don't really want to say my age when it happened but I was pretty young) before she was with my brother. Messy, I know.
Last weekend, I went out drinking with my gf (weve been together almost 2 years), my brother, his gf and a few others. I woke up to being kissed. I assumed it was my gf but it was actually my brothers gf. We were both naked in bed. I can't remember the sex but my ex said ive improved so much, best sex she's had etc.
I've no interest in her and I really do like my gf and I hate myself for what I did. I tried telling her yesterday but I couldn't. I have got a sex health test because I don't know how safe we were – can't remember anything. I don't want to break up but obviously she deserves better. Dont get me started on the fall out that will occur with my brother.
I just need some advice on how to tell her? I have tried but I can't.