There’s a lot to unpack here.
First of all I understand yours fears in respect of being cheated on and I also struggle to commit to the idea of having children.
There’s a million and 1 things that could go wrong in life, not just in relationships, but really the question is do you want to let your fears rule your life?
Would it be worse to try being in a relationship that might not work out for any reason, or be alone forever because you’re not willing to risk it? As they say, it’s better to have loved and lost than never have loved at all.
Life will never run perfectly, and you can never make any decision with 100% certainty of the outcome. That 100% only ever comes with hindsight.
At the moment what you’re doing is called catastrophising, something I also do a lot and have to constantly work at. It’s assuming and imagining the worst out comes.
There comes a point where you have to accept you can’t control everything in life.
Rather than asking yourself ‘what if this bad thing happens?’, change it to ‘what if it all works out?’ Or ‘what if it turns out to be the greatest decision I ever made and I get everything I ever wanted?’
I’d highly recommend a counsellor as they can help you and give you tools to work through these difficult mind processes. Ultimately you’ve learned a certain way of thinking and have to unlearn it.
Best of luck 😊