Everybody finds backwards lemons much more difficult than forwards ones. Everybody. I can remember exactly how impossible they felt when I first started - and that was 40 years ago! But the feeling when you get the hang of them and find you can do lots of them, stop and then start again is indescribably fabulous. Few things top it. Trust me.
Technique-wise, your hockey player friend isn't helping you by telling you to lean forwards towards the toes (I am assuming here that you're wearing figure skates but I could be wrong) and the video is much more to the point with the v-shape and pushing the feet outwards. In order to get the blades to glide, you need to have your weight in the right place and for backward lemons, that place is slap bang in the middle of the blades, not the front. In most of skating, you need to be aware of where your weight is and as the head is the heaviest part of you, it needs to be centered over your hips and they need to be centered over your feet and blades in order for you to have the best chance of (a) gliding properly and (b) not falling over.
The trick to backward lemons is not letting the feet go out too wide; the further they go out, the further you have to drag them back in. You need lots of knee bend and use your thigh muscles to push your feet out from that v-shape just a short distance before pulling them back in to have the heels of the blades approaching a v-shape. Rather than letting the heels touch, however, you need to bring the feet back parallel and then toes into the v-shape again so that you can do the next lemon. It's slow and painful to start with and feels nigh-on impossible, but I promise you that it is possible and you will do it!
Try to work on a rhythm that sees you bending your knees as you push outwards and straightening them as you drag the feet back inwards. If it helps, you can hold the hands of a friend who skates forwards and gives you a gentle push and steadying hand to help you get the feeling of the feet going out and coming back in again. Be careful not to put any pressure on that friend's hands, though. Do not be tempted to lean and have them hold you up and push you back - you need to use your own leg muscles and balance. If you're not holding the hands of another skater, then keep yours out to the side, at hip or waist height to help you balance.
It can also help to enlist a friend to watch your back, as many people find actually moving backwards terrifying. As you progress, it's easier to see behind you as most backwards skating involves looking behind you and pretty much moving sideways as much as backwards, but those lemons are blind.
Good luck.