Hi Johnny and welcome to our forum community;
I really feel for you. Sexuality can be very grey (not black and white) which can throw us. We turn to the one's we love thinking that being honest is best, which more often than not leads to upheaval.
Your situation isn't unique believe it or not; we get posts like yours at least once a week. So please don't feel you're odd because it's just not the case.
I want to assure you you're probably not gay as you would've known long ago. You may just have bisexual leanings ok; this is perfectly normal. I identify as bi and only spoke about it for the first time at 55.
The issues you face are complex. As Croix (above) has spoken about, your marriage is really important. Asking yourself what you actually want is necessary to move forward. If a single life as a bi man is it, then plan. If your marriage is what you want, then seek help. You can't do this alone...
In our 'Gender and Sexuality' Section, there are many threads dedicated to this very sensitive issue. Please look there and read as much as you can. Some are better than others, but they're full of posts from men who've gone thru it and some from men just starting their journey. I'm sure you'll be enlightened and helped by doing so.
Talking with your GP will definitely help, as they can refer you to a counsellor or psychologist. This type of pressure, if not addressed, can see you suffering depression or anxiety. Best to seek help now than down the track when it's too late to go back.
Don't forget you can always post about your pain and confusion ok. If you do, keep it to this thread instead of others you might come across as we can find you much easier.
I wish you well hun. Take care and be gentle on yourself; we genuinely care...