What possessed me to binge(or overeat)?

It's a survival response from eating too little

Let's go back a million years. Our ancestors then, Homo erectus, had no idea what a calorie was, or how much they should eat. They had to hunt, gather or scavenge their food. If they went for a while without getting enough, they had no way to know that they weren't eating enough, so they had this survival response, whereby if they go for a while (like days to weeks) without eating enough, when they found an unusually large amount of food (compared to what they'd been finding lately, because they didn't deliberately deprive themselves of food) they would eat as much as they could. They didn't know that this was a good idea to help them get through the food shortage, they just had this urge to keep eating more and more of it, until it was all gone. Another survival response they had, was obsessing about food, so they'd spend a lot more time looking for it, so they'd be more likely to find enough to survive.

We're descended from all the Homo erectuses that survived food shortages, hence we've inherited the same survival responses as they have. In our modern society, surrounded by too much food and with an obesity epidemic, they can be a real pain in the behind, because they're what causes so many diets to fail. It does my head in when people go on about "survival mode" and only discuss metabolic adaptation (e.g. adaptive thermogensis), and completely ignore the normal behavioural and psychological responses that we have as a result of eating too little. And these tend to kick in earlier than any physiological/metabolic responses.

The fact that this is happening (including your constant craving for carbs - cravings are another survival response to insufficient foods, Homo erectus didn't know what vitamins, protein etc to eat, so if they weren't getting enough of something, they'd crave it, and that would make them go out and try to find it) suggests that you're not eating enough generally. It may help to raise your calories a little, it may not need to be that much, e.g. 100 cals/week extra may be enough. But the idea is to find the "sweet spot" in terms of daily calories, where you're losing weight at a slow yet steady rate, but you're also eating enough that these kinds of survival responses don't start kicking in. This is what's most sustainable in the long term, and what matters isn't how fast you get to goal, it's staying there for life.

note: yes I'm aware that some binge eating is purely emotional/psychological, but in this case the OP hasn't mentioned a history of this, and also, purely emotional binge eating happens even when you're not restricting calories. (plus I wouldn't call several slices of bread a binge... more like unintentional overeating) If someone is finding that they only have a problem with binging or the desire to overeat only when they are dieting, then the problem is most likely to be that they're eating too little.

You know what, after weeks of failure (yes, this isn't the first time. I also overeat every weekend and I often pig out when I come home), I'm starting to think that my caloric intake may just be too low. I find it odd though, because a month ago I ate ~1300 cals everyday without a problem. I didn't really feel hungry going by that amount I mean I still occasionally indulged but for the most part I didn't have too much of a problem and I certainly didn't have frequent binges like the one I had today.

maybe your daily activity levels have changed., e.g. you're on your feet more. You may not even have noticed this. Maybe the temperature has dropped and your body's using more energy to keep warm (you won't necessarily feel cold if this is going on) But it does sound like this is caused by eating too little. Try upping your calories by just 100/day to start with, and if you still have this issue, try upping them again. Also the advice to eat more protein is good.

if your reason for being meat free is only about your carbon footprint, you could try to get locally farmed meat. Transporting food long distances has more of an environmental impact than whether you eat meat or eat vegetarian. In fact a lot of vegan and vegetarian foods are imported, or made in factories with imported ingredients. Eating local not only reduces your carbon footprint by a lot, you also help to support local farmers and the local economy.

Also, what about eggs? they're not meat and they don't contain lactose.

Are you lactose intolerant or allergic to milk (sorry if that's a stupid question but a lot of people on the internet say "lactose intolerant" when they mean "milk makes me ill" but don't know what it is in the milk that's making them ill, lactose intolerance is a specific problem with the sugar in milk (lactose)). If you're lactose intolerant you should be able to eat some kinds of dairy products without getting ill, i.e. those low in lactose. If you're allergic to the protein in milk, then that makes things a lot more difficult, although knowing which milk protein (i.e. whey or casein) you're allergic to may help, e.g. if you're allergic to whey but okay with casein you may be okay with casein based protein supplements (and vice versa).

Thanks for telling me about that! I'll try to look more into local food products. I do eat eggs for now.

I was never officially diagnosed, but I get stomach cramps and indigestion when I drink milk.The same would happen with certain brands of yogurt and cream cheese. For the most part (especially if I don't eat this in the morning), I can eat cheese and solid yogurt (like greek yogurt, but never the liquid ones).

that sounds like lactose intolerance rather than milk allergy. You could look up which other dairy products are low in lactose

greek yoghurt is lower in lactose as the watery part of it is drained off with cheese cloth, which contains most of the carbohydrate, while the protein part stays in the cheese cloth. i.e. it's high in protein and low in carbs compared to other dairy products. in dairy products, carbs = lactose. So it does sound like you're lactose intolerant and fine with milk protein.