Well for starters, it's good that you acknowledge being bi and are okay with that and all. It's important to never deny who you are.

That said though, first of all what is your "history" with homosexuality? Been around a lot of homophobes in your life? Hear a lot of religious shit? I grew up in a fiercely Catholic environment and it took me YEARS to shake off the guilt and worry that I was a dirty evil sinner. But with time and experience and introspection, you get past it and realized "why the hell did I let myself be so brainwashed by them?"

Or how about your GF? How long you been together? Are you REALLY okay with being in an open relationship? Can you live with the fact that she sees other guys or that you are seeing others instead of her? Are you at a point or have you ever reached a point where you'd just rather be with her than with some random guy? "Gay guilt" and "relationship guilt" are two different things, despite being easy to confuse, so make sure you differentiate here.

Maybe it's the guys you're seeing. Are you hooking with random strangers off some app? Cuz lets face it, we all feel gross about that on some level :p