I think @YellowAsteroid suggestion for small steps is a good one.
Personally I'd find a quiet space with something to write with and on and make a list of how I want my life to look in the next year to 5 years, who is in it and where.
If that includes your DH and living in the arrangement you have now then you are already living the life you want and are truly happy, that's not sarcasm I've met many non-conformist couples who seem to be quite happy. If not then you will need to make some pro and con lists for what you think you might want your furture to look like, in this you need to only consider your happiness, this can be difficult when you are worn down by situations which I suspect you are.
An architect I heard speak once said he approaches his planning by removing all the walls and considering only what was needed and then what was wanted. I thought that was a great way to approach a new project and it stops me thinking "inside the walls" that are already there. It is strange to consider things through "without walls" to begin with but once you realise that you can find ways around those "walls", all the things that seem set in stone and improve them, it makes way more sense to start with a completely blank canvas and chuck everything out of your life and add back in what you really need and want.
There are few people who are completely blameless when a relationship breaks down. The thing to remember is that you are not a relationship expert no one is, you recognise you make mistakes, we all do, none of us are perfect. Accepting the blame for some of the things that have happened is healthy, sometimes we try and see too much of the other persons view though and end up carrying more of the blame ourselves than we need. Lots of relationships have mismatched sex lives, the solution isn't finding a 3rd, 4th, or 5th person to get involved with the one partner, nor is it always exploring kinks. Some partners who love their spouses but find their sex life frustrating put their sexual energies into non-sexual things for example rather than run off to be "tutored" by a sex worker ... I'm really curious as to what that is!