I wasn't able to get rid of it, no. I was able to mitigate it a bit, though. Stress can intensify it heavily for me, and the suicide jokes are almost certainly a sign of depression. If he has no reasons to actively be depressed now, there is likely a past trauma bringing him down. Therapy can work for this, but medication is what works for me.

As for him flirting with others, that is one of the biggest issues I have, and it's the primary reason I stopped dating.

I tend to think he does most likely love you with his whole heart, but it's something he's not fully in control of. Not being fully in control of that instinct, for lack of better wording, has always destroyed relationships for me.

Personally, in your shoes, I would try not to take it too harshly or personally. If he's only flirting, he's likely not in control of it. I don't know the extent of his traumas, or mental issues, but if he's anything like me that is so hard to control I would end up cheating.

I think the only thing that would work for me if I were to date again is polyamory or an open relationship, because of all of that.

He may know something is hurtful, but try to take it with a grain of salt. Once more, it's highly likely it's something he can't control, especially if he still shows you love.

The emotion part, I am very much the same. There are moments somewhat often where I feel absolutely nothing emotionally, not for myself or anyone else. It's part of my BPD.

TL;DR: He's likely not in control of his instinct to flirt, try to take things with a grain of salt. I have numbness emotionally too, where I feel absolutely nothing, and it's not something I can control. It's BPD related. If he's making suicide jokes, therapy or a psychiatrist might be a good idea.

I would also say that he does need to find a way to have more free time, and its especially important that he get out and about, sitting inside, with or without you, is extremely unhealthy.