Hi there @MrBig2015 and welcome to the forum. Widowed bi guy speaking.
I’m going to start off by saying that I second everything @AJSTAR has said: he’s bang on the money. However, if he doesn’t mind, I’m going to suggest a little finesse-tweak to one sentence of his reply:
“I often get guys on Grindr who are bi or straight”
I’d change that to read “I often get guys on Grindr who are bi or who think of themselves as straight” - cos (in my book, anyway) if a guy says “I’m straight” then opens a Grindr account looking for sex with other men… he’s NOT STRAIGHT!
Of course, it’s not mine or anyone else’s place to tell you what your sexuality is - only you can discover that for yourself and decide what, if any, “label” feels like the best fit - but I hope you won’t be offended if I say that, based on what you’ve written in your post, I think you’re currently in a whole heap of denial.
It’s this business of you describing yourself as “not bisexual - just straight but curious” that gets me. I have issues with the whole concept of “bi curious”. I believe it’s a label used by people who ARE bisexual but who are having problems coming to terms with that truth. In my opinion, these people are queer but are afraid of accepting the fact or - god forbid! - identifying as such. I don’t blame them for feeling this way. Growing up, as we all have to, in what is still an overwhelmingly cis/het society with its pressures to conform, the journey to self-acceptance as a queer person can be a scary one - but it’s one you have to make if you are to be truly at one with yourself. Anything else is living a lie, and that road leads nowhere but misery-town. Anxiety, depression, suicide… you name it. I’m not joking or being over-dramatic here. Denial kills.
Let’s have a look at what you posted. You mention that you took pictures of yourself in lingerie and posted them online because you “just wanted to tell someone or be accepted” - so did you post the pics on a dedicated forum for crossdressers? Nope: you posted them on a hook-up platform for gay men, and asked for cock pictures.
Elsewhere you are adamant that you are “not bisexual - just curious” - but there’s a world of difference between a genuinely straight guy idly thinking “I wonder what it must be like to do XYZ with another guy?” (in the same way that he might speculate on what it must be like to be a dolphin / have wings / live on the international space station) and what you’ve said. To quote your own words:
“I’d also ask for cock pictures and wanted to give a guy a bj as it would get me so horny”
“I find myself wanting to give a guy a bj, have sex with a guy as a bottom…”
“I find the urges becoming really strong of wanting to act on it and I dont know what to do…”
Those are not the words of a heterosexual man. They don’t speak of “curiousness”; they speak of NEED. Day in, day out, nature is telling you who you are, but you are steadfastly refusing to listen to it. The longer you refuse to listen, the louder and more insistent that voice will become until you either accept its truth or go nuts.
Please understand that in pointing out these things I’m not trying to attack you or make you feel bad. I’m trying to help you achieve happiness and be at peace with yourself. As others here have said, before you and your fiancée get anywhere near the idea of actually marrying, you need to get 100% honest with yourself and 100% honest with her. No more of this “I’m not really…” nonsense. If you love her, you owe it to her to tell her the truth - and (as many bisexual men before you have had to learn), if she’s not totally accepting of the fact that YOU CRAVE COCK, then she’s not the girl for you and you’re not the boy for her.