lonely but not alone

i have been in and out of relationships since i was 15, i have never been alone, yet i always end up feeling alone in relationships. whether i start to hide certain feelings because i don't want to upset my partner or whether it's because i'm extremely bad at communicating my thoughts and emotions and always feel on some level i will never be understood.
the beginning of a relationship for me is manic and obsessive, then either i make a mistake or some life change happens in the life of me or a partner, and then i become riddled with commitment anxiety.
any time i have ever been on a break i immediately start talking to people online. i get in this very weird aggressive mindset and become all the bad parts of myself, i have no shame. then the second "said break" ends, i feel immediate regret and guilt. (i even as a teenager i compulsively cheated on my hs gf with people online (only recently accepted it as cheating).
the guilt i will live with forever, but i'm also learning to be compassionate toward myself because no one can do better if they constantly feel like shit.

why can't i be alone? why do i need constant sexual attention and interaction?
does anyone else struggle like this? feeling lonely but never having an excuse for why? do you struggle with anxiety about commitment? or shame towards wanting more sexually from your partners than they can physically/mentally give you?

i feel bad for feeling lonely, as if i shouldn't be because i am never alone. i feel guilty, i feel shameful. i don't want to feel alone in a relationship, it doesn't make sense.

things 2 remember
i am strong, intelligent, caring, passionate, creative, loving, and brave. i am not my past. i can be a good person and i choose to be a good person. i am grateful for the people i have in my life.