I think I'm autistic... but why do I lie?

First off, I'm not new to the forum but, given the topic, I didn't want it linked to a username that could possibly come up on a search by people I know in the real world. 

For  background I am in my 30's and fairly sure I'm autistic, I was told it was likely by a medical professional in the field and having researched I fit almost all of the criteria to a tee. However there is an aspect that worries me I keep coming up against, and that's about lying. I keep seeing that Autistic people are usually honest to a fault, and in certain aspects that is me too, if someone asks an opinion I will either outright tell them what I think or if I think I'm going to be really mean I just say I'd prefer not to talk about it, but when it comes to explaining myself, what I'm feeling, how I'm coping, I lie, and a lot. 

I have seen the odd mention here and there about certain situations where this happens to autistic children but im struggling to find much info on it to see if I fit those criteria so I was wondering if this is anyone on here resonates with or if anyone knows where I can get more info on it?

If any of this sound familiar I would love the help, I'm waiting for my assessment when I intend to be entirely truthful about this but I'm getting stresses out because they want family members input and I don't know how they will go down, they're not wonderfully supportive at the best of times and I think if they're there I will struggle to be truthful.

Further Details - Its a bit long, sorry, but you can skip it with no issue if you already understand.

For those that want some more detail, basically what I'm talking about is for years I have been getting overwhelmed, anxious and upset in places where I'm told I should be having fun and I didn't know why and rather than tell people what was happening to me, because I didn't know, I would say I had a stomach upset or a headache or similar, however over the years as my reactions got worse and my ability to cope degraded I would have to make up a bigger lie and this escalated to the point where to cover for the fact I had basically quit my job been ghosting all my family and friends for months while I had a mental breakdown, shutdown, suicide attempt etc I said "I had cancer and I didn't want to tell them", it fit the pattern for them, they know id spent some time in hospital and then a lot of time healing and I certainly looked like id been dragged through hell and back, but ever since I've been wracked with guilt. And there's another couple of big lies for similar reasons, for example they think I have a diagnosed digestive issue that limits my diet to cover for me restrictive eating habits, this lie isn't actually that far from the truth because I do have digestive issues and cant absorb b12 or some other minerals, they're just not formally diagnosed because they couldnt figure out the cause, but I'm certainly not on a restrictive diet plan from the doctors, that's all my brain.

As contradictory as it seems I long for one of them to call me on it so I can just tell them what really happened, and this habit of being brutally honest if im called on a lie is normal behaviour for me, the odd times its happened people have been taken a back by how I don't try to hold the lie I just tell them the whole story and that maily because the lie tends to be a stess reaction and I regret it later.

So as far as where I think it may have come from I do have a theory. As a small child I spent much of my time with my grandparents who were difficult, my nan especially was verbally abusive and sometimes would find reasons to get my grandad to hit me and my sister for things she saw as bad behaviour, the bad behaviour was stuff like, struggling to spell, not understanding what she meant, not acting how she thought a child should act in front of her friends etc. I remember being very small and being terrified of my nan and having to find ways to cheat and lie about what I was doing and I suspect I masked quite early because of that too, and that continued for most of my pre-teen childhood. 

The first big lie I can remember telling to cover up was when I was 11 or 12 and I had a traumatic abuse situation happen (that I've still never admitted to anyone) and the only way I could get out of it and stop it happening without telling people was to outright lie and then I had to continue that lie to stay safe, very soon after I discovered my sexuality wasn't straight and due to homophobia in my family I lied about that too and so the cycle continues right up to the present day where I still have gender issues I cant talk about because of the backlash I'll receive. 

Anyway, sorry for that mind dump, I've moved it down here for those that want context.