Where did my happiness go?

Are there any of you out there that are perfectly happy single and yet when in relationships get completely miserable despite even perhaps being madly in love with the other half?

Is there something about being in a relationship that you just can’t handle?
Have you resigned yourself to being alone because that makes you happier?
Do you lose a sense of self when you are with someone?

This isn’t quite the sum total of my relationship and feelings currently – my relationship is lets just say far from healthy and probably why I’m miserable…but I’m wondering if it’s a kind of self-sabotaging thing perhaps???

It was going really well and now it’s not…and whilst it’s not all my fault I wonder whether just deep down i don’t WANT to be in a relationship…maybe…