I learned to love by being loved first.
My little baby sister loved me when nobody else did and I learned how to care for her, about her and how to love her. I also had this lady who would sometimes feed me when my parents didn't and she told me she loved me. And after I while, I loved her back.
I think it is possible to love someone else even if you don't completely love yourself.

But I also believe that there is a kind of distorted love - that is a bit like obsession for a person that we want in our lives, that we think we can't live without, who gives us what we need and don't have etc. This love is usually very one sided and not satisfying after a while BECAUSE - and here is the complicated thing - the problem with loving someone but not loving ourselves is that while we want that person to love us back so very badly, we don't think we deserve it, we think we are not good enough, not worthy enough etc. It is hard to accept the love for what it is. So the result can be to stay clingy, desperate for someone to love us and every little criticism or drawback makes us vulnerable and afraid of losing that love.
So loving ourselves is important for healing and freedom, I strongly believe that.