If you feel unlovable as an adult the likely reason why is that your primary caregivers were unwilling or unable to love you as a child. But we need only look at family situations that tend to produce happy, healthy, well-adjusted people to see why blaming yourself is wrong thinking.
Parents who can and do love their kids love them before they’ve done anything to merit this love. Any baby could get switched into that situation and, assuming the parents believed it was theirs, the result would be the same, the baby would be loved deeply. In this sense we can view parental love, especially in those important formative years where secure attachment is established, as a sort of projection. It has much more to do with the caregiver’s capacity to love than it does with the child’s fitness to receive that love.
When most hear ‘well-adjusted’ they immediately attribute this adjustment to the person in question but when I hear ‘well-adjusted’ I attribute this adjustment to the controlling environment. It’s not people who do the adjusting, it’s people who are adjusted based on environmental contingencies in the form of positive and negative reinforcements.
All those ‘lovable’ people out there were given love freely and deeply, without any strings attached. They attribute their self-confidence and adjustment to themselves without stopping to consider that their thoughts, feelings, and behaviors would likely be much different had they grown up in less favorable circumstances.
The controlling environment is important, but where behavioral psychology ends is where existential freedom begins. You cease being a machine manipulated by your environment and become a person when you increase your awareness around how your set of environmental contingencies has shaped your perceptions and behaviors so that you can freely decide on how you are going to be in the world despite these controlling contingencies. Everyone is lovable, not everyone grew up in conditions where they were loved though. In adulthood the question becomes how to create those conditions yourself, which starts with believing that you deserve them.