My FA and the past 10 years. Would love thoughts.

kisstheviolets, this focus is all on him and not on yourself. I know you're working with a therapist already, but as you can see, no one he's with is "enough" for him so there's no point in further scrutiny.

Here's the thing. If someone is unhappy with themselves and looking for the "one" to fix that, they'll never be in a stable, functional, and healthy long-term relationship. They just want a bandaid / distraction so they can feel good without doing difficult healing work and being okay with themselves. Short cut! That can't last because it's not fixing the core reasons for that person's damaged relationship with themselves. And if you can't be complete on your own and require other people to fill your voids (and yes, this can apply to anxious or avoidant, though the voids and needs are different in each), then you'll never be able to comfortably make the decision to commit for the long-haul.

A healthy relationship is about getting to know someone and choosing to be on a team with them. It's about mixing inter- and intra-dependence to make life easier and more fulfilling. It's not about someone being enough for someone else, because a healthy person is foundationally enough for themselves but still wants to share with another person (or persons). It's not about finding another person to meet all your needs so you don't have to meet them on your own. There's no "one" -- there's actually several you may be compatible with, or there's none if you're emotionally unavailable, lack true vulnerability, and don't consciously make the decision to be open to a reciprocal relationship.

I know you feel stuck and are trying to let go but aren't there yet. Your ex isn't your real problem, which is why you're still endlessly ruminating. There's something from before your ex you need to heal. Once you do that, you won't "need" him, and you'll be able to feel more confident about choosing people who also choose serious relationships (assuming that's what your goal is).

Insecure reasons or not. Having secret relationships, being deceptive, lying, cheating, and going behind someone's or multiple people's backs. That's someone who is not worth a single minute of time and will never be a reciprocal and committed partner for anyone until they seriously work on themselves and break those habits, if they ever get to the point they are willing to. It kind of surprises me how long people can act out patterns like that without any sense of awareness or something that finally makes them change. I just don't understand the point of making a commitment and relationship with someone if you don't want to be committed. It's much easier to be single and non committed if you don't want to be truly attached to anyone and date or see as many people as you like, honestly.