Siwmae,
I’m a Welshman and I’ve just started learning with this course, because I only know how to speak English and have a C2 in Spanish. The fact that I wasn’t offered to learn Welsh in my school really annoys me, as I really love our language and the history behind it. I sometimes feel less Welsh for not being able to speak it properly and it saddens me that it will never be my “mother tongue”. Does anyone else that is Welsh have these types of feelings?
Yes, that’s a familiar feeling for me too, but I’ve found that over time it’s possible to re-work some of that guilt into a positive.
The thing to remember is that not being offered Welsh in school (I wasn’t either) and it never being your first language (nor mine) is a consequence of history, not your fault, and not things that can be changed now. BUT you are learning it now, so whilst you can’t change the past, you can certainly embrace the present and future by becoming a Welsh speaker and reaping the benefits of the wonderful ‘parallel world’ that that exposes you too.
In fact, in my experience, there are quite a few elements of learning Welsh without those ‘head-starts’ that even appear to be advantages - from a deeper understanding of the hurdles new learners face because you’ve gone through them yourself, to helping first-language Welsh colleagues with their formal English email writing! 
I suspect we all do to an extent and for many of us is the reason we started to speak Welsh here. However it isn’t our fault as individuals it is as Siaron says it’s a consequence of our history, yet this feeling persists. It led me to delve into my own family history to uncover why my paternal family stopped speaking Welsh. It seems my great-grandfather in around the 1920s on a Carmarthenshire farm had seven sons, one of whom being my grandfather, decided to stop using Welsh in the home. The probable reason is that he felt it would be more useful for his sons to gain greater proficiency in English as most of his sons would be seeking work off the farm [it has since been shown that this was not a useful thing to do]. Probable as this seemed to be a prevalent argument at the time. So for my family, Welsh skipped a few generations until I took up the baton with SSiW.
I’m English and did French and German at school, but it always saddened me that we weren’t offered Welsh when Wales was the closest country to us (I’m from the Wirral).
I did beginner’s Welsh while I was at Aberystwyth university and recently I have completed Say Something in Welsh (new and old courses) plus the Duolingo Welsh course.
I now live in Wales and would love to speak the language proficiently, although accept that I’m never going to speak it as well as those whose mother tongue is Welsh.
I don’t think you should feel guilty. You’re trying to spread the use of the language now. I think a lot of Welsh speakers have a certain amount of respect for those of us who attempt to learn Welsh later in life. Concentrate on how much you have learnt and enjoy expanding your knowledge, rather than beating yourself up about something which is not your fault.
It’s frustrating and feels very unjust doesn’t it? But not speaking Welsh doesn’t make you any less Welsh. If you come from South Wales like me, then you’re part of an amazing culture and heritage which is unique and reflected in the languages and dialects spoken here. It’s great that you’re learning to speak Welsh as it opens the doors to a whole new world. But don’t let anyone think you’re not Welsh enough!
Yes I agree with Elinor, there is no need to feel any guilt about not being able to speak Welsh. I have friends who dont speak Welsh who are more patriotic than some I’ve met who do speak Welsh. If you are learning, persevere at your own pace and dont give up, some things that are worthwhile take time, ‘Dyfal donc a dyr y garreg’.
And as St David said, ‘Gwnewch y Pethau Bychan’.
Paul
I was born and brought up in Cardiff to non-Welsh-speaking parents. Although we learnt Welsh at school until I was 10, it was very rudimentary and I left school remembering very little. I don’t feel guilty for not speaking the language - just saddened that it wasn’t given more importance in high school. I learnt French and German but don’t remember Welsh even being an option! I’m now trying restore that lack through the SaySomethinginWelsh course. As I now live between Spain and Cornwall I have little chance to practice face-to-face conversation but hope to stun everyone I meet with my outstanding proficiency next time I go back to my roots for a visit!!!