OP if he has fire arms then you really need to call the police if he threatens to do anything, either to himself or to you. I doubt very much that he’d do anything to himself, but a man who has weapons can sure make things difficult for you.
Men like this have their own image of themselves, completely separate from what anybody else thinks of them. What other people think hardly even matters, because what they perceive is all ldictated by the way they view themselves and how they think others should react to them. It matters not what you feel, or how much you love him, because all he sees is that you are an accessory to him. He knows what he’s doing and he’ll continue to do it until you break the cycle. At the moment the consequences of him cheating and not keeping promises is that you go quiet for a day, and he knows the price of that is a few soppy words and a bunch of flowers. In extreme circumstances he knows that threatening to kill himself will bring you back, so to him it’s a simple equation, do what he wants, make some conciliatory noises to you, or if you’re being difficult threaten to kill himself, then job done. He gets to do what he likes and he gets to keep control over you.
In order to get away from him you need to stop this cycle. When you do unfortunately for you you’re then into unknown territory and you don’t know what he’ll do. The fact that he has guns turns that from a risky situation into a potentially very dangerous one indeed. The sooner you intervene by calling the police the better. An emotionally invested man who feels his dignity has been taken away, and who has weapons at his disposal is a very serious situation.
I don’t mean to scare you, but the two factory ou need to consider is, does he feel that his pride and dignity is being damaged, and what ability does he have to create problems if he feels that they have. He has guns, so he has the ability, and if he’s so desperate to keep you in line then almost certainly he will feel slighted by your rejection. To this end I think you’d be very sensible to get the police involved at the first available opportunity if there’s even the slightest hint of him acting rashly or with heightened emotion.
As I have already said, the chances of him killing himself are very slim indeed, and it’s not your decision or your responsibility if he makes that choice, but while he has weapons both the opportunity to intimidate you or indeed harm you are greatly increased.
Keep in mind that there is a marked difference between an intimidation and a threat. An intimidation is designed to get a response, to get him what he wants. Come back to me or I’ll kill myself. He’s not saying he is going to kill himself, he’s using the threat of killing himself as leverage to get you to do what he wants. It doesn’t mean he’s intending to do it, it means that he thinks that you will comply to avoid the potential consequences. In either case you need to call the police, immediately, or even call 101 in advance if you think he will be trouble. As PP have said, you can’t control what he does, so don’t rely on the assumption that you can, because once his threats of suicide fail, he’ll move onto trying other things. The very last thing you need to be facing is trying to escape the attentions of a man who has guns, and who is not afraid to use them to intimidate, so you really need to call the police straight away if you’re in any doubt at all. Don’t squash down your worries by trying to minimise or rashonalise, just call them.